Grendel LMG

[stanc]

I think the only real environment for the Grendel to gain traction in is amongst the Eastern European Countries that are aware of the Russian threat, while NATO leaves them out to dry. The biggest issue for them is that 5.56, 7.62 NATO, & 7.62x54R are the dominant cartridges in their small arms inventories, with 7.62x39 on its way out in many cases, along with 5.45x39 being displaced by 5.56 NATO. Poland, Czech Republic, Slovakia, and Hungary have formed a new military alliance separate from NATO since they see the writing on the wall.

...the biggest and most important factor that would make the Grendel get noticed is if a modern LMG was chambered in it, and shown to provide the same downrange benefits as 7.62 GMPG's such as the PKM and MAG58, only from a much smaller package.

The adoption of the Grendel in Eastern Europe would already have a logistics framework in-place for brass and ammo with Lapua and PPU from the North and South, but weapons and magazines would be the main new items to be purchased. Selling points for budget-strapped countries:

* Longer barrel life
* One-caliber small arms system potential
* Longer weapon life with lower chamber pressures
* Inherent accuracy potential
* Existing framework for ammunition components
* Existing framework for barrel blanks in 6.5mm, a popular European bore
* Existing framework for projectiles

The most recent breath of fresh air is the observation by LRRPF52 that some East European countries might develop an interest in the cartridge. Let's help him pursue that notion and see where it takes us.
Okay. What can we do in that regard?

It looks to me like the only practical option to prove the concept is to Grendelize an RPD light machine gun, then put it up against a vz59 or PKM.

That would be rather expensive, though, so I'd suggest a more modest first step: Buy an RPD belt and see how well (or poorly) 6.5 Grendel rounds fit in it.

IMO, a second (or parallel) step would also seem prudent: Do comparison testing of 6.5 FMJ vs 7.62 FMJ. Comparing barrier penetration and other characteristics would confirm or refute the idea that a 6.5 LMG can deliver the desired performance.

If those steps produce acceptable results, then consideration can be given to acquiring and converting an RPD. (Perhaps a Grendel Guild project? Maybe DSArms could be convinced to help?)

Comments? Other proposals?


http://www.youtube.com/watch?v=dQiU_82HKpk

[RangerRick]

Here a link to a belt site:

http://www.blackrivermilitaria.com/belts.html

Scroll down to see the RPD belt.

Type Control-+ to zoom in and control-0 to reset the browser to normal size.

[stanc]

Thanks, Rick. Unfortunately, that site is apparently just informational. It says the items shown are not for sale.

But, DSArms lists two 50-rd belts with a drum for $24.95

http://www.dsarms.com/RPD-Drum-And-Belt-Package---RPDDB/productinfo/RPDDB/

I haven't found anyplace where one can buy a single RPD belt, let alone a 10-link segment like I'd need here in Kalifornia.

[RangerRick]

Thanks, Rick. Unfortunately, that site is apparently just informational. It says the items shown are not for sale.

But, DSArms lists two 50-rd belts with a drum for $24.95

http://www.dsarms.com/RPD-Drum-And-Belt-Package---RPDDB/productinfo/RPDDB/

I haven't found anyplace where one can buy a single RPD belt, let alone a 10-link segment like I'd need here in Kalifornia.

Yeah, that was just for comparison, but the pictures are crappy compared to the ds arms site. The sides of the link don't look terribly sloped so they may work with the Grendel. The part of the link that supports the neck will be very loose, though. Don't know if it will cause trouble or not.

[RangerRick]

But, DSArms lists two 50-rd belts with a drum for $24.95

http://www.dsarms.com/RPD-Drum-And-Belt-Package---RPDDB/productinfo/RPDDB/

I haven't found anyplace where one can buy a single RPD belt, let alone a 10-link segment like I'd need here in Kalifornia.

All I saw was a 100 round belt and drum, but I ordered it. If you can't have that belt in CA I can cut off 10 rounds worth and send it to you.
If the belt works out OK, maybe we can take up a collection to get a semi-auto RPD ($2,100) and get them to make one of their barrels in 6.5 Grendel.

When I get the belt, I'll load it up with Grendel brass and see how it looks.

Rick

[stanc]

The sides of the link don't look terribly sloped so they may work with the Grendel.
Yeah, it might. Won't know until somebody actually tries it.

The part of the link that supports the neck will be very loose, though. Don't know if it will cause trouble or not.
It doesn't appear to contact the neck at all, so there shouldn't be any trouble in that aspect.

http://i41.photobucket.com/albums/e266/bigmegina/rpdlink01.jpg

But, no matter. It's obvious from the complete lack of response to this thread that nobody is interested in advancing the idea of 6.5 Grendel for Eastern Europe, not even the person who originally proposed it, or the one who called it a "breath of fresh air" that we should help pursue.

[stanc]

All I saw was a 100 round belt and drum, but I ordered it.
The ad says 100-rd belt, but if you look carefully at the photo, there's a 50-rd belt in the drum and another 50-rd belt outside. I don't know if 100-rd belts were even made.

You can see in the video above there are two, 50-rd sections, with one falling off as he's shooting while walking, then the second section falls off when he's firing prone.

If you can't have that belt in CA I can cut off 10 rounds worth and send it to you.
If the belt works out OK, maybe we can take up a collection to get a semi-auto RPD ($2,100) and get them to make one of their barrels in 6.5 Grendel.

When I get the belt, I'll load it up with Grendel brass and see how it looks.
Oh, crap. Didn't know you were gonna do that. I should've made my previous post earlier today, before you spent the money. Rats! :(

[bwaites]

Some of us ARE interested, but just don't have a lot to contribute or time to post after we do everything else we are supposed to do! But...we are more than willing to contribute financially to advancement of the ideas!!

[JASmith]

OK, can you expand on the caption for post #6?

It looks like at least part of the belt is metal -- is there cloth there too?

There isn't much in the way of explanation ---

[stanc]

There's no cloth. Entire belt is metal. I'm not sure what else you wish to know?

http://www.dsarms.com/images/RPDDB.jpg

[LRRPF52]

RPD drum, non-disintegrating metallic link. Those links look more difficult to manufacture than the NATO disintegrating links.

I'll tell you, right now, if I was in a gunner position, I would take a Grendel LMG over a SAW or M240 position without reservation, even not knowing the 500m plus terminal performance of even a mediocre 120gr FMJ. I have a feeling every gunner I've known would feel the same, as well as the current guys serving in that capacity.

[stanc]

RPD drum, non-disintegrating metallic link. Those links look more difficult to manufacture than the NATO disintegrating links.
As do the non-disintegrating links for the vz59 and PKM 7.62x54R machine guns. But, the RPD and its non-disintegrating link belts seem to be the only readily available option to demonstrate the viability of a 6.5 Grendel belt-fed LMG.

I'll tell you, right now, if I was in a gunner position, I would take a Grendel LMG over a SAW or M240 position without reservation, even not knowing the 500m plus terminal performance of even a mediocre 120gr FMJ.
Yeah, but if this idea is ever presented to the V4 militaries as a proposed replacement for 7.62x54R/7.62x51, don't you think it likely they'd want to see equal (or at least near-equal) terminal effects?

The Norma 120gr FMJ is certainly not the best 6.5 ball projectile that could be used in comparison tests with the 7.62 rounds, especially since standard 7.62x54R ball has a steel-core bullet. It's a pity the Swedish 6.5x55 steel-core AP bullets can't be had for such testing.

[bwaites]

The Norma 120gr FMJ is certainly not the best 6.5 ball projectile that could be used in comparison tests with the 7.62 rounds, especially since standard 7.62x54R ball has a steel-core bullet. It's a pity the Swedish 6.5x55 steel-core AP bullets can't be had for such testing.

They are too heavy for the Grendel anyway. To be fair, you need a 120'ish grain Grendel steel core bullet.

[stanc]

They are too heavy for the Grendel anyway.
Hmm. Perhaps you're thinking of the (139gr) lead-core Ball projectiles? IIRC, the steel-core AP bullet is only 113 grains.

To be fair, you need a 120'ish grain Grendel steel core bullet.
That'd be longer than a Lapua 144gr FMJ, and use up too much powder space.

I dunno what the optimum weight would be for a steel-core 6.5 bullet, but it looks to me like 110 grains would be about max.

[LRRPF52]

The Visegrad 4 have already been looking at new weapons systems. Polish Grom have been heavily influenced by a tight working relationship with certain elements in the US Spec Ops community, and the days of AK's and Vz58's are limited as these guys have felt the weight difference between an M4A1 w/ SOPMOD, and an AK with rails, light, Aimpoint, etc. The AK's days are numbered in Eastern Europe. It's already unacceptably front heavy in 1947 and 1953 forms, let alone with modern accessories attached. The Kreb's kits and Brugger & Thommet rails make an AK an even more ungainly beast of an Assault Rifle.

I don't see a need for them to load the same projectile for assault rifles and LMG's anyway, since they have had different end-user logistics packages for PKM's, MG3's, Vz's, SVD's, AK74's, MPi-AKS-74N's, Tantals, and so forth. A steel rod penetrator like the 7N6 or 7N10 would be great, with plenty of lead weight, and a thin projectile jacket. There is zero reason to have a strictly belt-fed LMG use the same projectiles as a mag-fed AR.

V4's biggest driver is Poland right now, and they have gained a lot of real-world operational experience in GWOT with their special forces and airborne units in Iraq and Afghanistan that the Russians simply have not. As I have worked with other nations in the region, I'm advocating them to either look at rebarreling existing rifles in inventory as the bores die, or adopting a new carbine entirely. No significant developments have been made as far as Light Machineguns are concerned since the Ultimax 100, and to a very limited extent, the KAC LMG. It gets overlooked too often, due to the distraction of trying to "fix" the Armalite/M4/Colt Commando...the one weapon system that isn't broken and is highly-favored by units that can choose whatever they want, literally, since no later than 1961, and is still the main go-to individual carbine in SAS, SBS, SF, NAVSPECWAR, Ranger Regiment, MARSOC, Force Recon, LRRPS/LRS, and a host of other countries' special ops where the M16 family is not their primary service rifle.

One of the biggest limitations is the lack of much development in the private sector regarding LMG's, because everyone wants to tinker with carbines and rifles, versus belt-fed. We'll see how it goes. I know what cartridge I would build around right now...

[LRRPF52]

The Baltics and Finland are long overdue for a modern LMG and Assault Rifle/Carbine with modern accessory integration architecture. Estonia is using a bunch of Galils the Israelis dumped on them, along with MG3's in 7.62 NATO. Finland is using the out-of-production Rk95 in 7.62x39, some ancient 7.62x39 mag-fed LMG and PKM's. Latvia and Lithuania have had AKS-74 variants, but the Lithuanian SF really like paratrooper SAW's with modernized kits in A-stan. The region is way overdue for some weapon upgrades for certain, especially when you compare the turn of the century from the late 1800's into the 1900's, and look at the quantum shifts in small arms development generated by Maxim, Browning, and Garand...metallic cartridges had already become dominant in the later 1800's in pistols, and were taking over rifle chamberings. With us at the year 2011, which corresponds to the century-ago 1911, I wonder how we're doing compared to that era. The cased telescoping tech is the biggest thing I think, if it can be successful, especially for dismounts. That would be our era's quantum leap.

This is why the modular weapon system approach is the best avenue to pursue, so operating system and feed can be upgraded as the technology advances. Either way, I think we'll actually see some developments happen in the next two decades, where the AK will be looked at like a Mauser or Mosin Nagant, but still be around of course. The AR will continue to influence designs as far as ergos and modularity are concerned, and accessory integration will be the trend most sought after by developed countries. Who knows if metallic cartridges will be in cutting-edge weapons...

[bwaites]

Hmm. Perhaps you're thinking of the (139gr) lead-core Ball projectiles? IIRC, the steel-core AP bullet is only 113 grains.



The 6.5 AP Projectiles I have came from 6.5x55 ammo, and they weighed considerably more than 113 grains before I machined them down. I couldn't get decent velocities with them, only about 2300 FPS, and they wouldn't penetrate 1/2" steel. I've machined them down to 108 grains by trimming the tails, so we'll see what happens.

[stanc]

The 6.5 AP Projectiles I have came from 6.5x55 ammo, and they weighed considerably more than 113 grains before I machined them down.
Interesting. Are you sure your bullets don't have tungsten cores?

I was going by info on the Swedish military ammo website for weight of the steel-core AP, so I can't verify the accuracy of the 113gr figure.

[LRRPF52]

A steel penetrator design based off the 7N6 or 7N10 would facilitate the same velocities as a standard FMJ. Just look at the 5.45x39 velocities for those at 2900 fps out of a 16.3" barrel, with projectile weights at 56gr. M4 with M855 62gr out of 14.5" barrel is 2900+ (not the British down-loaded weak ammo for the L85, but full-power M855). A 120gr 6.5 running quick with the narrow steel rod would smoke some steel. A 130gr LMG load could also be considered, with the right powder. Personally, I wouldn't want crazy penetration in AR's unless dealing with body armor, in which case you would need extreme velocity and light projectiles with small penetrators. Those would have limited effectiveness at distances past 400-500, whereas a standard weight projectile would break through mud, brick, and earthen barriers better out of an LMG. I don't want that for my door-kickers...too much blue on blue.

Either way, you're looking at no less than 4 different projectiles for the dismount force logistics structure: Standard AR load, Standard LMG, AP, Tracer. Notice we haven't even covered DM/Sniper, which is where this cartridge really shines as well, with the 123gr Scenar/SMK types.

[stanc]

The Visegrad 4 have already been looking at new weapons systems.
I know the Czechs are fielding the CZ805, but I couldn't find any indication that Poland or Hungary were planning to replace their AK variants.

The Kreb's kits and Brugger & Thommet rails make an AK an even more ungainly beast of an Assault Rifle.
No kidding. Hungarian AK63 MF
http://26.media.tumblr.com/tumblr_lp8s0gPatA1qarjbyo1_500.jpg

I don't see a need for them to load the same projectile for assault rifles and LMG's anyway... There is zero reason to have a strictly belt-fed LMG use the same projectiles as a mag-fed AR.
Granted, but isn't that what everybody does (except the Chinese)?

[bwaites]

Interesting. Are you sure your bullets don't have tungsten cores?

I was going by info on the Swedish military ammo website for weight of the steel-core AP, so I can't verify the accuracy of the 113gr figure.

Well, I can check again, but I'm pretty sure they were magnetic.

Going to be next week, though, I'm in the middle of a garage/loading room remodel.

[RangerRick]

A college room mate of mine is a retired Army bird Colonel. He was a Special Forces Officer and Polish speaker. He helped the Poles set up their Special Forces school as a special project right before he retired.

If we get anywhere with this I can approach him about a contact point there.

I have a belt on order from DS Arms. I'll post picks with Grendel brass and 7.62x39 brass in it side by side. I'll load up some Norma FMJs to 2.205 and see how much powder we can get in.

Rick

[stanc]

A steel penetrator design based off the 7N6 or 7N10 would facilitate the same velocities as a standard FMJ.
I haven't seen a sectional view of the 7N6 and 7N10, but in any case, what I was thinking of is the use of mild steel cores in 7.62x54R ammo, and the possibility that the V4 would also use the same construction in bullets for 6.5 Grendel, should they adopt it.

Just look at the 5.45x39 velocities for those at 2900 fps out of a 16.3" barrel, with projectile weights at 56gr. M4 with M855 62gr out of 14.5" barrel is 2900+. A 120gr 6.5 running quick with the narrow steel rod would smoke some steel.
Maybe, but you're not going to get anywhere near 2900 fps with a 6.5 120gr. According to Bill W, in a 19.5" barrel the 123gr SMK ammo from Black Hills did only 2550-2575 fps, and he considered that a hot load. If MV is kept down to 2500-2525 fps, it'll only be doing ~2400 fps from a 14.5" tube.

Either way, you're looking at no less than 4 different projectiles for the dismount force logistics structure: Standard AR load, Standard LMG, AP, Tracer.
IMO you're being optimistic about getting two different Ball loads adopted, but otherwise I agree.

I think for the near term, what's most needed is a good Ball projectile, most likely non-fragmenting FMJ (assuming the V4 intend to continue strictly abiding by Hague Declaration III).

Notice we haven't even covered DM/Sniper, which is where this cartridge really shines as well, with the 123gr Scenar/SMK types.
True. That's for another thread, perhaps.

[bwaites]

You may already be aware that some 6.5x55 FMJs had steel jackets, which would also be attracted to a magnet.

Unless there is a copper colored steel, these have a copper jacket, lead inside the base, and a steel tip. The bottom of the projectile is not magnetic, as I recall.

[stanc]

Unless there is a copper colored steel...
Steel jackets can be copper colored. There are gilding metal clad steel (GMCS) jackets, and copper washed steel jackets.

...these have a copper jacket, lead inside the base, and a steel tip.
Let me get this straight. Does it have a short, steel tip (with long, lead base slug) similar to M855 Ball?

Or does it have a long, steel core with pointed tip (and a small lead plug at the base)?

The bottom of the projectile is not magnetic, as I recall.
If it won't stick to the jacket at the base, then it must not be a steel jacket.

[JASmith]

Using the expression KE Density = (1/2)MV²/(πR²) (where M=mass, V=velocity, and R=bullet radius) I find that the Grendel is about 100 ft/sec shy of matching the 7.62X51 M80 potential for perforating steel plates for lead-core FMJ bullets in the 100 - 120 grain class.

Replacing all or part of the lead with a hardened pin as is done with the M855A1 would change this to the extent that the Grendel with a 20-24 inch barrel might just be able to perforate the same thickness of steel as the M855A1.

Of course we would need to test. Before that, someone needs to design and fabricate steel-cored 6.5 bullets in the 100-120 gr weight range, develop safe loads and verify with load development testing. Then, at last, we could see if the Grendel might do as well.

Any takers on bullet fab?

In the meantime, I'm happy with knowing that the Grendel is close and maybe good enough!

[stanc]

Of course we would need to test. Before that, someone needs to design and fabricate steel-cored 6.5 bullets in the 100-120 gr weight range, develop safe loads and verify with load development testing. Then, at last, we could see if the Grendel might do as well.
Or, we could do comparison tests with the lead-core Norma 120gr FMJ vs 7.62x54R (or 7.62x51) lead-core FMJ. That would let us see how well Grendel can do now, instead of waiting years for someone to design and fabricate steel-core bullets, then develop and verify safe loads.

In the meantime, I'm happy with knowing that the Grendel is close and maybe good enough!
Personally, I'd rather see proof, than depend upon a maybe.

[JASmith]

The the 7.62X51 NATO kind of clones the velocity for bullet weight of the 7.62X54R in bullets of the 140 - 175 grain class. (As an aside, the NATO round appeared about 60 years after the Russian round - talk about progress!)

Since we're already pretty sure the Grendel doesn't quite get the needed energy density to punch the same plate as the .308, we should be surprised if it does any better against the Russian round.

Why test when one is reasonably sure the outcome isn't what you want? The bullet designs suggested will likely 'prove' what we already know. That will do nothing to help...

One more time -- Inappropriate testing is likely to be harmful to keeping the momentum going.

[RangerRick]

I don't see a need for them to load the same projectile for assault rifles and LMG's anyway, since they have had different end-user logistics packages for PKM's, MG3's, Vz's, SVD's, AK74's, MPi-AKS-74N's, Tantals, and so forth. A steel rod penetrator like the 7N6 or 7N10 would be great, with plenty of lead weight, and a thin projectile jacket. There is zero reason to have a strictly belt-fed LMG use the same projectiles as a mag-fed AR.


I would disagree with this if you can't fire the LMG rounds in the rifle and vice versa. If you have different rounds, the zero would be different and that would negate the whole point of ammo commonality.

I know I've stripped rounds from 7.62 belts for M-14 sniper rifles when we ran out of sniper ammo. I also know of guys who gathered up expended links and assembled belts for the machine guns when they only got rifle ammo resupply.

Things can get chaotic sometimes.

It may be a moot point as all of these countries are now in Nato and will likely refit with Nato standard ammo when they refit, except perhaps Special Ops forces.

[RangerRick]

Or, we could do comparison tests with the lead-core Norma 120gr FMJ vs 7.62x54R (or 7.62x51) lead-core FMJ. That would let us see how well Grendel can do now, instead of waiting years for someone to design and fabricate steel-core bullets, then develop and verify safe loads.

Personally, I'd rather see proof, than depend upon a maybe.

The 7.62x54 is more powerful than the 7.62x51 NATO. It is closer to the 30.06. So the comparison would favor the x54.

The idea is that you can have a light machine gun of acceptable power with much less weight and ammo commonality with your rifles. The comparison should be the RPD in 7.62x39 and the RPD in Grendel.

You could do the x54 comparison for reference, but no way will the Grendel match it, even at long range.

You can demonstrate the weight difference, though. The Grendel ammo will be much lighter than the x54. As a percentage even more than the x51.

[RangerRick]

Sounds good.

Cool. By chance did they give you a delivery date?

Not yet, but the money is gone from my checking account so it better be soon!

R

[JASmith]

I would disagree with this if you can't fire the LMG rounds in the rifle and vice versa. If you have different rounds, the zero would be different and that would negate the whole point of ammo commonality.

I know I've stripped rounds from 7.62 belts for M-14 sniper rifles when we ran out of sniper ammo. I also know of guys who gathered up expended links and assembled belts for the machine guns when they only got rifle ammo resupply.

Things can get chaotic sometimes...

You make an interesting point. I think we are almost on the same page. One could visualize that a Grendel used by a sharpshooter or sniper would likely be shooting long range precision ammo with ballistics similar to those desired for the LMG.

This would be different than using M855A1 in an M4/M16 when the sharpshooter runs out of Mk262 but more or less equivalent with your description of the M14 and general purpose MG.

And yes, things get chaotic and there are times when the ammo you got is the ammo you use...

[stanc]

Since we're already pretty sure the Grendel doesn't quite get the needed energy density to punch the same plate as the .308, we should be surprised if it does any better against the Russian round.

Why test when one is reasonably sure the outcome isn't what you want?
To gain knowledge. Without testing, we do not actually know what the outcome will be. If nothing else, test data for the current bullet would give us a baseline to guide improvements.

One more time -- Inappropriate testing is likely to be harmful to keeping the momentum going.
Momentum? What momentum??? Momentum implies movement. How are we any further along than we were in 2005? Did some momentus development occur while I slept last night?

[JASmith]

...Without testing, we do not actually know what the outcome will be. If nothing else, test data for the current bullet would give us a baseline to guide improvements...
I am beginning to despair of finding the words to communicate a basic truth:

Absent a federal contract we are guaranteed to have tests that won't be credible except for those people who want to denigrate or destroy the Grendel.

This truth should not keep us from seeking tests but it should absolutely keep us from doing tests that we can reasonably expect to produce disappointing results.

[stanc]

The 7.62x54 is more powerful than the 7.62x51 NATO. It is closer to the 30.06. So the comparison would favor the x54.

The idea is that you can have a light machine gun of acceptable power with much less weight and ammo commonality with your rifles. The comparison should be the RPD in 7.62x39 and the RPD in Grendel.
I disagree. As I read it, the proposal by LRRPF52 is for a Grendel LMG "to provide the same downrange benefits as 7.62 GMPG's such as the PKM and MAG58." Since he also notes the potential for a one-caliber system using 6.5 Grendel, that means it would have to be good enough to not only replace 7.62x54R in the V4 armies, it would have to be good enough to not be outranged by the PKMs used by the Russian army (the threat for which the V4 nations created a military alliance).

You could do the x54 comparison for reference, but no way will the Grendel match it, even at long range.
I don't know if it's necessary to match terminal performance, although the closer we can get to equal performance, the better. More importantly, I think it's vital to match effective range, for the reason noted above.

You can demonstrate the weight difference, though. The Grendel ammo will be much lighter than the x54.
Absolutely, a comparison of weapon and ammo weights should be part of any presentation.

[stanc]

I am beginning to despair of finding the words to communicate a basic truth:

Absent a federal contract we are guaranteed to have tests that won't be credible...
Well, I know the feeling. I can't get you to understand that I'm talking about informal tests only to tell us where we stand at present, while you keep equating it with formal tests done for officialdom at some point in the future.

They are not the same thing, and the one is no less "credible" than the other. The formal testing you advocate has its place, but it isn't necessary in the early stages.

This truth should not keep us from seeking tests but it should absolutely keep us from doing tests that we can reasonably expect to produce disappointing results.
Since we're talking 120gr @ 2500-2550 fps, or 110gr @ 2600-2650 fps, versus 150gr @ 2750 fps, I'd say we can reasonably expect "disappointing results" regardless of what 6.5 bullet is tested...

[stanc]

Here's another reason why I think there should be comparison testing with the Norma 120gr FMJ.

The logical evolution of this project is the conversion of a belt-fed RPD to 6.5 Grendel. That will likely require financial support, either a lot of money from a few backers, or a smaller amount from many individuals.

Now, I can't speak for others (like Bill W, who's expressed an interest), but I know that before I'd commit my hardly earned cash to such a project, I would want to see evidence that it had some chance for successfully achieving the goal. That's why my OP stipulated two prerequisites: (a) Buy an RPD belt and see how well 6.5 Grendel rounds fit in it; (b) Do comparison testing of 6.5 FMJ vs 7.62 FMJ.

The rationale for (a) should be obvious. If the cartridges don't fit in the belt properly, there's no point in buying an RPD.

My reasoning for (b) is that it'd show relative performance with bullets of the same type. If terminal effects of 6.5 Grendel with lead-core projectiles isn't close enough to that of 7.62x54R with lead-core bullets, it'd be illogical to expect relative capability to be any better with steel-core bullets in each caliber, so again there'd be no point to buying an RPD.

However, if 6.5 Grendel rounds appear to fit okay in the 7.62x39 links, and if terminal effects/barrier testing showed at least the promise of near-7.62x54R performance, then it would be worth proceeding.

Rick has gambled $30+ of his own money to check (a). We can wait to see how that turns out, before taking the next step.

[JASmith]

...If terminal effects of 6.5 Grendel with lead-core projectiles isn't close enough to that of 7.62x54R with lead-core bullets, it'd be illogical to expect relative capability to be any better with steel-core bullets in each caliber, so again there'd be no point to buying an RPD...

Surprise! We don't need or want to equal or better the 7.62X51 bullet for bullet.

Performance of the 7.62X51 M80 round is the standard we are using. Even the pipsqueak M855A1 is claimed to be able to defeat some armors at least as well as the M80. And yes, those claims are supported by government or government-sponsored tests.

If steel-cored 6.5 bullets from the Grendel can equal or better both the M80 and M855A1 performance, then we have a case.

We are very sure that the lead-core FMJ won't get through the plates as well as the M80, or we would likely have already seen pictures of the event.

Let's look for testing that will build a case. Do it privately so that that case can be properly articulated with the right people. The testing will still not be viewed as credible because it won't be official, but it gets our foot in the door.

[stanc]

Surprise! We don't need or want to equal or better the 7.62X51 bullet for bullet.
I said nothing about doing better than 7.62x51. However, equal is desirable, and "close enough" is essential.

But, I do think you are mistaken about the "bullet for bullet" part. If each bullet type (Ball, Tracer, AP, Sniper, etc) doesn't give performance comparable to those of 7.62x54R/7.62x51, then the V4 militaries are unlikely to go for the idea.

If steel-cored 6.5 bullets from the Grendel can equal or better both the M80 and M855A1 performance, then we have a case.
Unless you have credible information that the V4 plan to use M855A1, its performance would seem to be irrelevant.

The pertinent round to compare against is Russian 7.62x54R.

We are very sure that the lead-core FMJ won't get through the plates as well as the M80, or we would likely have already seen pictures of the event.
Illogical conclusion. For one thing, nobody can photograph an event that hasn't happened. For another, until somebody actually shoots steel plates, cinder blocks, etc, with 6.5 FMJ, we can't know how it fares in that regard.

Let's look for testing that will build a case. Do it privately so that that case can be properly articulated with the right people. The testing will still not be viewed as credible because it won't be official, but it gets our foot in the door.
The "foot in the door" part is something I've argued all along. Glad to see you're finally coming around.

But at present, building a case to present to "the right people" is both unnecessary and premature. That can and should wait until optimized 6.5 bullets have been designed and fully developed.

What we need right now is to build a data base so that we can make decisions based on factual information, not beliefs or wishful thinking.

[stanc]

A steel penetrator design based off the 7N6 or 7N10 would facilitate the same velocities as a standard FMJ. Just look at the 5.45x39 velocities for those at 2900 fps out of a 16.3" barrel, with projectile weights at 56gr. M4 with M855 62gr out of 14.5" barrel is 2900+ (not the British down-loaded weak ammo for the L85, but full-power M855). A 120gr 6.5 running quick with the narrow steel rod would smoke some steel.
Okay, you confused me with the "narrow steel rod" comment. The 7N6 or 7N10 design is what I had in mind.

(53gr 7N6 below. 56gr 7N10 reportedly has a longer steel core.)
http://www.cruffler.com/Features/OCT-01/545-CrossSection.jpg

If I calculated correctly, scaling up would make a 6.5mm "7N10" bullet weighing 97 grains, with ~1.24" length. A little tweaking could probably increase weight to 100 grains, without increasing length. Such a lightweight bullet could be pushed @ ~2750 fps from a 20" barrel, thereby matching 7.62 muzzle velocity. But, would BC be high enough to match 7.62 trajectory?

Lengthen the bullet to the 110gr "sweet spot" for 6.5 Grendel, and it'll extend much deeper into the powder space, causing a double whammy against MV. Would the increased BC of the longer, heavier bullet be enough to offset the reduced velocity?

[JASmith]

...But at present, building a case to present to "the right people" is both unnecessary and premature. What we need right now is to build a data base so that we can make decisions based on factual information, not beliefs or wishful thinking.

So we want to 'voodoo' the Grendel into being good enough by hoping the tests will magically be good enough?

You clearly don't believe the facts as presented. Find another ballistician who can help you and the rest of us.

[stanc]

So we want to 'voodoo' the Grendel into being good enough by hoping the tests will magically be good enough?
Now, there's a moronic statement. I said nothing about hoping. I said I'd like to see actual test data, rather than just speculation.

You clearly don't believe the facts as presented.
What facts? You haven't presented any facts. All you've done is make silly statements, like the "voodoo" one above, and "that the lead-core FMJ won't get through the plates as well as the M80, or we would have already seen pictures," and "we have to build a case to present to the right people" (even though there's nothing on which to build a case), and "inappropriate testing is likely to be harmful to keeping the momentum going" (even though there's no momentum to keep going).

Find another ballistician who can help you and the rest of us.
That's fine by me. All the present one wants to do is write requirements documents. :rolleyes:

[RangerRick]

I disagree. As I read it, the proposal by LRRPF52 is for a Grendel LMG "to provide the same downrange benefits as 7.62 GMPG's such as the PKM and MAG58." Since he also notes the potential for a one-caliber system using 6.5 Grendel, that means it would have to be good enough to not only replace 7.62x54R in the V4 armies, it would have to be good enough to not be outranged by the PKMs used by the Russian army (the threat for which the V4 nations created a military alliance).

I don't know if it's necessary to match terminal performance, although the closer we can get to equal performance, the better. More importantly, I think it's vital to match effective range, for the reason noted above.

Absolutely, a comparison of weapon and ammo weights should be part of any presentation.

OK, I see what you are getting at. We just have to demonstrate that we have an equivalent effective range, not equal terminal effects.

How do we define effective range? 50% hit probability was the U.S. Army definition assuming you had the ability to disable the target at that range.

I think we'll have at least as good hit probability, but how do define disabling ability?

[stanc]

OK, I see what you are getting at. We just have to demonstrate that we have an equivalent effective range, not equal terminal effects.

How do we define effective range? 50% hit probability was the U.S. Army definition assuming you had the ability to disable the target at that range.
Perhaps "effective range" was not the best term to use. What I'm thinking is that the trajectory should be at least as flat as for 7.62x54R.

The challenge will be to design a FMJ bullet with BC good enough to achieve that trajectory, when launched at a MV for which the cartridge is capable.

I think we'll have at least as good hit probability, but how do define disabling ability?
Good question. I don't know if there is a generally accepted definition.

Maybe it'd be best to just show gel tests comparing wound channels of 6.5 Grendel and 7.62x54R?

The old gel test of the Norma 120gr FMJ does look very similar to Fackler's wound profile of 7.62x54R. It's conceiveable that a FMJ bullet optimized for 6.5 Grendel could do significantly better than 7.62 at closer ranges. At long distances (over 400 meters), Gary Roberts says there's no real difference between different calibers.

[RangerRick]

Sounds good.

Cool. By chance did they give you a delivery date?

Belt should be here (North Carolina) by Wednesday. I'll get your 10 round segment in the mail ASAP.

Rick

[RangerRick]

Perhaps "effective range" was not the best term to use. What I'm thinking is that the trajectory should be at least as flat as for 7.62x54R.

The challenge will be to design a FMJ bullet with BC good enough to achieve that trajectory, when launched at a MV for which the cartridge is capable.

Good question. I don't know if there is a generally accepted definition.

Maybe it'd be best to just show gel tests comparing wound channels of 6.5 Grendel and 7.62x54R?

The old gel test of the Norma 120gr FMJ does look very similar to Fackler's wound profile of 7.62x54R. It's conceiveable that a FMJ bullet optimized for 6.5 Grendel could do significantly better than 7.62 at closer ranges. At long distances (over 400 meters), Gary Roberts says there's no real difference between different calibers.


The data I've found suggests that the service round projo is 148 grains at 2723 fps. The cartridge seems to be capable of more than that, but maybe that's only in modern bolt actions and not military weapons. The Sellier & Bellot 150 grain FMJ goes 2840 fps out of a 28 inch barrel. That's very similar to the 7.62x51 and we know the Grendel comes close to matching those ballistics.

The Hornady .312, 150 grain FMJ only has a BC of .361, their 150 grain boat tail FMJ has a BC of .398, so we have them beat there for lead cores. Steel cores of the same weight would almost certainly have higher BC's because of the length.

That looks to be the biggest advantage of the x54: lots of room in the case for long bullets because of fairly low powder loads relative to case size.

With the higher sectional density we may be able to make up what the bullet lacks in weight to get similar penetration capability, particularly at longer ranges.

I have a buddy with a Mosin Nagant I could probably borrow to do tests, but my range only goes to 300 yards.

At what range do we need to demonstrate plate penetration?

[JASmith]

Isn't it interesting that the US managed to duplicate in 1955 the performance of a round developed in the 1890s?

[RangerRick]

Looking at the picture of the belt it looks like the tab by the bullet with 7.62x39 rounds may be there to guide the head of the case as it is stripped out of the belt, not the neck.

It clearly doesn't touch the 7.62x39 case neck.

If that's the case, it bodes well for smooth functioning with Grendel cartridges.

Rick

[RangerRick]

"Isn't it interesting that the US managed to duplicate in 1955 the performance of a round developed in the 1890s?"

Yes, but it's in a case 2/3 the length, allowing shorter actions and vastly simplifying gas operated systems, which means lighter guns. Compare the Browning 30 to the M-240 or M-60.

Rick

[RangerRick]

I wonder if Bill A would be interested in this? I'm sure he'd like to see the Grendel Cartridge in a belt fed system.

Demonstrating that the relatively straight walled cartridge works in a belt fed system would be a plus for him.

If nothing else, maybe we could get him to let us use some of his test facilities.

Rick

[JASmith]

"Isn't it interesting that the US managed to duplicate in 1955 the performance of a round developed in the 1890s?"

Yes, but it's in a case 2/3 the length, allowing shorter actions and vastly simplifying gas operated systems, which means lighter guns. Compare the Browning 30 to the M-240 or M-60.

Rick
Your point is well-taken. The rim also complicates feeding in automatic weapons. Your observation helps illustrate why we need to avoid a one-dimensional focus on any one characteristic.

It also helps show how things can get complicated real fast.

The way development folks deal with the complexity is to write a list of characteristics the new thing needs to have to be useable as a replacement for the old thing. That list, when formalized, becomes a requirements document.

Cheers!
Joe

[stanc]

The data I've found suggests that the service round projo is 148 grains at 2723 fps. The cartridge seems to be capable of more than that, but maybe that's only in modern bolt actions and not military weapons. The Sellier & Bellot 150 grain FMJ goes 2840 fps out of a 28 inch barrel. That's very similar to the 7.62x51 and we know the Grendel comes close to matching those ballistics.

The Hornady .312, 150 grain FMJ only has a BC of .361, their 150 grain boat tail FMJ has a BC of .398, so we have them beat there for lead cores. Steel cores of the same weight would almost certainly have higher BC's because of the length.
http://7.62x54r.net/MosinID/MosinAmmo.htm shows MVs and BCs for various 7.62x54R military and commercial loads in different barrel lengths. Not sure how the BCs were arrived at (Perhaps they used two chronographs?), as some seem ridiculously low, while some others look excessively high.

I have a buddy with a Mosin Nagant I could probably borrow to do tests, but my range only goes to 300 yards.

At what range do we need to demonstrate plate penetration?
I think it'd be good to do it at 100, 200 and 300 yards, if the 7.62 ammo has boat tail bullets, like 150gr Wolf Gold and Prvi http://7.62x54r.net/MosinID/MosinAmmo029.htm

If you use ammo with flat base bullets, like the 148gr Wolf load http://7.62x54r.net/MosinID/MosinAmmo017.htm , perhaps only 100 yards, since it'd lose velocity too rapidly at the longer ranges.

Many years ago, I shot 1/4", 3/8" and 1/2" mild steel plates at 100 yards, using 7.62x51 M80 and 5.56x45 M193. The 7.62x51 punched holes through the 1/2" plate at that distance, so it seems likely that 7.62x54R also would.

Since I don't know what thickness of mild steel 6.5 Grendel and 7.62x54R will penetrate at 200 and 300 yards, if you decide to test at either of those distances, I'd suggest shooting at 3/8" and 1/4" in addition to (or in place of) a 1/2" plate.

If you feel like it, I'd also like to see a CMU (hollow cinder block) shot at 100 yards with both calibers.

Rick, if you're willing and able to do these tests, I'll gladly pay for the mild steel plates, cinder blocks, and ammo.

P.S. Take good, hi-res photos, please.

[JASmith]

<sigh>
You aren't the only one who I am communicating with in this thread...

[RangerRick]

I think it'd be good to do it at 100, 200 and 300 yards, if the 7.62 ammo has boat tail bullets, like 150gr Wolf Gold and Prvi http://7.62x54r.net/MosinID/MosinAmmo029.htm

Many years ago, I shot 1/4", 3/8" and 1/2" mild steel plates at 100 yards, using 7.62x51 M80 and 5.56x45 M193. The 7.62x51 punched holes through the 1/2" plate at that distance, so it seems likely that 7.62x54R also would.

Since I don't know what thickness of mild steel 6.5 Grendel and 7.62x54R will penetrate at 200 and 300 yards, if you decide to test at either of those distances, I'd suggest shooting at 3/8" and 1/4" in addition to (or in place of) a 1/2" plate.

If you feel like it, I'd also like to see a CMU (hollow cinder block) shot at 100 yards with both calibers.

Rick, if you're willing and able to do these tests, I'll gladly pay for the mild steel plates, cinder blocks, and ammo.

P.S. Take good, hi-res photos, please.

Where is a good source for the plate?

[stanc]

Where is a good source for the plate?
I used to buy them at metal scrap (salvage? surplus?) yards. Check the yellow pages for your area?

[JASmith]

Make sure you use plates from the same sheet.

We had trouble correlating test results with computer predictions on some destructive tests a few years back. I asked for tensile tests for the steel used in the structure. The results showed that the steel had a yield strength about 50% greater than the nominal yield strength for mild steel. The predictions went a lot better when the proper material responses were modeled.

This disparity in yield strength will confuse your penetration results.

I'm assuming you won't want to pay for a test laboratory to assure that the different sheets have the same strength, so getting the plates from the same sheet will at least assure uniform comparisons.

[stanc]

Make sure you use plates from the same sheet.

I'm assuming you won't want to pay for a test laboratory to assure that the different sheets have the same strength, so getting the plates from the same sheet will at least assure uniform comparisons.
A very good idea if more than one plate of a particular thickness is to be used. But, if Rick decides to shoot at only one distance, then only one plate will be needed. OTOH, if he elects to shoot at more than one distance, it'll probably require one plate each of different thicknesses.

I'm thinking that 7.62x54R lead-core FMJ should punch through 1/2" mild steel @ 100 yards, but it may be necessary to drop down to 3/8" @ 200 yards, and 1/4" @ 300 yards, in order to get full penetration.

[JASmith]

Just to clarify: The target plate will likely be about 6X6, 12X12, 18X18, or 24x28 inches, depending on convenience and range.

The parent plate from which the target plate is cut is generally much larger. I have rarely seen them larger than 4' wide, but they can run 8-12 ft long. Longer is doable, but handling the plate gets to be a bit of a challenge.

So, depending on what is found, there is a possibility of getting several target plates from one parent plate. These should have pretty much the same properties. Not always, but usually close enough for our purposes. Yeah, even this gets complicated when you don't want to unintentionally mislead or confuse yourself or your audience.

A RELATED POINT:

As a rule of thumb, try to keep the hits more than 1-inch from the nearest edge. (Three or four times the plate thickness or bullet diameter, whichever is larger)

The metal will have some heat-induced changes in properties near the edge if torch cut. Also, the plate will respond differently to hits near even a saw-cut edge because of edge effects.

[RangerRick]

Hi Guys,

Got the RPD belts and drum today. Stan, your 10 round section should go in the mail tomorrow.

I put some Grendel rounds loaded with Nosler 120 grain FMJ's in the belt as well as some new IMI 7.62x39 brass.

The belt seems to work great. The link only has a slight taper. This makes sense because the head of the cartridge has to slide through it when loading.

Of course, mechanisms can be boogered up by small changes, so we will have to see.

This first picture shows the loading tab on the right. Moving right to left the first case is a 7.62x39, followed by an empty Grendel case followed by a loaded Grendsel round. The empty slot was because of a bent up link.

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02777.jpg



These are pics of the belt loaded with a few Grendel rounds and 7.62 cases:

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02778.jpg

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02779.jpg

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02781.jpg

continued in part 2.

[JASmith]

Nice work!

The Grendel in those belts looks like it is at home and positively lethal!

[RangerRick]

There is a larger gap between the tab on the front and the brass with the Grendel as you would expect. It looks like that tab is used to position the link, not align the bullet. They were pretty beat up by the feed mechanism.
http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02786.jpg


Four Grendel rounds (on right) in a row beside four 7.62 cases.

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02794.jpg

[RangerRick]

Various close up views of the belt.

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02795.jpg

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02796.jpg

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02799.jpg

[RangerRick]

This is the connector link between the two 50 round belts. There is a lead belt (on the right in the picture) and a tail belt. The lead belt has the loading tab and ends with part of a disintegrating link.

It looks to me like you could make a whole belt out of these disintegrating links. It wouldn't be as flexible as the wired together links, though.

The tail belt begins with the second part of the disintegrating link, and ends with a small metal tube link. That helps you wind up the belt so it fits in the drum. It probably also dampens whiplash of the last round and locks the bolt open.

I was a little surprised that you couldn't make an infinite belt like with the NATO disintegrating link, but without a quick change barrel, I guess it forces you to let the barrel cool a little while loading a new belt.

Since the RPD is a squad machine gun, it was not meant for sustained auto fire like the bigger guns.

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02801.jpg

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02802.jpg

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02803.jpg

more of this in part 5

[RangerRick]

Pictures of assembles lead and tail belt:

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02804.jpg

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02805.jpg

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02806.jpg

[RangerRick]

Here is the case head end of the links with both the lead (on right) and tail belts showing . Notice that the tail belt is different from the lead belt. Instead of a detent that fits in the extractor groove, it has plate that is behind the head of the cartridge.

I guess that would prevent the round from getting pushed backwards out of the belt. I don't know if the lead and tail belts are different in all 100 round belts, but I suspect one is a newer design and we just happened to get a mix of the two.

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02809.jpg



Here is the last link in the tail belt.
http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02810.jpg



The last two pics are of the belt and drum. These 120 FMJ's were loaded to mag length for a Grendel. They had plenty of room. We might have to load to AK mag length (2.205) if we want to have interchangeability. I don't know if the longer rounds will feed, but they fit in the Drum OK.

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02816.jpg

http://i670.photobucket.com/albums/vv69/rfincher1/RPD%20Belt/DSC02817.jpg


RR

[stanc]

Here is the case head end of the links with both the lead (on right) and tail belts showing . Notice that the tail belt is different from the lead belt. Instead of a detent that fits in the extractor groove, it has plate that is behind the head of the cartridge.

I guess that would prevent the round from getting pushed backwards out of the belt. I don't know if the lead and tail belts are different in all 100 round belts, but I suspect one is a newer design and we just happened to get a mix of the two.
You're right on both counts. The starter belt is the original Russian design. The other belt is the later Hungarian design, meant to keep rounds from backing out, which tended to happen after belts were reused several times.

The last two pics are of the belt and drum. These 120 FMJ's were loaded to mag length for a Grendel. They had plenty of room. We might have to load to AK mag length (2.205) if we want to have interchangeability.
That's probably unnecessary. When I first brought it up, it had slipped my mind that AKs are made in 5.56x45, which has the same OAL as 6.5 Grendel. My bad.

Looks good, Rick. Ya know, this just might work! :cool:

[RangerRick]

That's probably unnecessary. When I first brought it up, it had slipped my mind that AKs are made in 5.56x45, which has the same OAL as 6.5 Grendel. My bad.

Looks good, Rick. Ya know, this just might work! :cool:

Yes, I'm very encouraged. The Grendel brass I used was all Lapua fired several times, so it's worst case, since new brass is a little smaller.

There didn't appear to be any warping of the links with the bigger cases. The open portion just opened a tad wider at the front and the closed portion didn't deform at all.

It was a little tighter than the 7.62 brass, but not much. So, I don't think the bolt will have any problem stripping it out of the belt.

This particular belt is a little bent up in places so we'll have to straighten it up a little before use, or get a new manufacture one.

RR

[bwaites]

Ok, I'm a little confused. Take a loose tolerance machine gun and shoot Grendel ammo as just a proof of concept? Is that the idea?

I'll predict that you'll make it work, at least part of the time, and maybe you'll get lucky and it will run great, but to what end? No one is going to put that machine gun back into production because the cartridge works, and from I understand, most of those machine guns have been and are worn out.

If all you are proving is that you can make the Grendel work from links, well, I have no doubt it can be done. Lots of other cartridges work, there is no reason to believe that it won't, simply because it hasn't been done.

I wonder about making it work consistently not so much because of the links, but because the gas system will be far from ideal for the Grendel, the reciprocating mass is not optimized for the cartridge, etc.

We all have pet hobbies and desires though, so I wish you well! :)

[RangerRick]

If all you are proving is that you can make the Grendel work from links, well, I have no doubt it can be done. Lots of other cartridges work, there is no reason to believe that it won't, simply because it hasn't been done.

I wonder about making it work consistently not so much because of the links, but because the gas system will be far from ideal for the Grendel, the reciprocating mass is not optimized for the cartridge, etc.



The problem is a lot of other people do doubt that it can be done because the cartridge doesn't taper enough, or the shoulder angle is wrong, etc., etc. You can argue with those people forever, but if you can demonstrate a working system, it answers the basic questions.

Also, if you show that it can work in an ancient Soviet belt fed design, and in an AR platform, then the cartridge is flexible enough to be of interest.

As for the reciprocating mass, couldn't the same thing have been said about the AR platform?

[bwaites]

The problem is a lot of other people do doubt that it can be done because the cartridge doesn't taper enough, or the shoulder angle is wrong, etc., etc. You can argue with those people forever, but if you can demonstrate a working system, it answers the basic questions.

Also, if you show that it can work in an ancient Soviet belt fed design, and in an AR platform, then the cartridge is flexible enough to be of interest.

As for the reciprocating mass, couldn't the same thing have been said about the AR platform?

Understand on the doubters!

As for the AR platform, to some extent you are correct. Thus all he research into proper gas port sizes, etc.

The problem is that ancient Soviet belt fed has such loose tolerances you could probably make anything close work at least sometimes!

Good luck, though!

[stanc]

Ok, I'm a little confused. Take a loose tolerance machine gun and shoot Grendel ammo as just a proof of concept? Is that the idea?
Is it just to prove that a 6.5 Grendel machine gun can be built? No.

I'll predict that you'll make it work, at least part of the time, and maybe you'll get lucky and it will run great, but to what end? No one is going to put that machine gun back into production because the cartridge works, and from I understand, most of those machine guns have been and are worn out.
I imagine that's true, but the purpose isn't to show that the RPD can be upgraded to 6.5 Grendel.

I wonder about making it work consistently not so much because of the links, but because the gas system will be far from ideal for the Grendel, the reciprocating mass is not optimized for the cartridge, etc.
Before Bill Alexander began tinkering with the AR15, it wasn't optimized for 6.5 Grendel, either. We can't know for sure if the RPD can be successfully converted until somebody with the necessary knowledge and experience makes the effort.

We all have pet hobbies and desires though, so I wish you well! :)
It isn't a hobby, pet or otherwise. It's an attempt to achieve a specific goal.

A week and a half ago, Paul opined that the best chance for 6.5 Grendel to become a military cartridge is to interest the V4 nations -- Poland, Hungary, Slovakia and the Czech Republic -- in adopting it, and the "most important factor that would make the Grendel get noticed is if a modern LMG was chambered in it, and shown to provide the same downrange benefits as 7.62 GMPG's." http://www.65grendel.com/forum/showthread.php?9-Grendel-as-a-Universal-Infantry-Cartridge&p=9181&viewfull=1#post9181

Joe suggested, "Let's help him pursue that notion and see where it takes us." http://www.65grendel.com/forum/showthread.php?9-Grendel-as-a-Universal-Infantry-Cartridge&p=9236&viewfull=1#post9236

When nobody else posted any ideas for "pursuing that notion," I started this thread. Since conversion of a modern LMG is not feasible for any of us (if only because there are no disintegrating links available), I proposed using the old RPD as a vehicle that could be used in side-by-side evaluations with OPFOR GPMGs like the PKM.

Paul had previously asked, "Have we already discussed the possibility of using RPD links for the Grendel?" http://www.65grendel.com/forum/showthread.php?9-Grendel-as-a-Universal-Infantry-Cartridge&p=9227&viewfull=1#post9227

Since the Europeans have long been using non-disintegrating links like those in RPD belts, that gave further impetus to the idea of converting an RPD to 6.5 Grendel.

Is it worth doing? I dunno, but it's the only idea I could come up with. If anyone else has alternative proposals that are feasible for us to develop, I'd be more than happy to see them.

[LRRPF52]

The main benefit of an RPD Grendel would be to demonstrate that converting existing systems is doable. I'm not sure if any of the Eastern European Countries are using any RPD variants anymore, since the RPK basically replaced it long ago in the Squad Automatic Rifle role, with 75rd drums for the 7.62x39, and 45rd mags for the RPK-74. Both of the designs don't have a quick barrel change feature, so their role is limited in sustained fire capacity, which is ok for short duration mission profiles such as raids. The RPD was very well-favored by the Rhodesian SAS, due to its compactness and firepower, as no other small belt-fed LMG's existed in the 1960's other than the Stoner 63 System, which they didn't have access to. The RPD is much too costly to produce compared to the RPK, so the USSR dumped it to reserve units as time went on.

Where you might get people's attention with an RPD Grendel is for those who might adopt the cartridge, while a new LMG is being developed. I bet most RPD bores are blown to ****, so a caliber change would not be so out of the budgetary considerations of a small, struggling state. The added benefit of denying your neighbors East & West from using your logistics would be a possible advantage, since many of those countries still use 7.62x39 & 5.45x39 Soviet cartridges.

An RPD/Grendel would probably need gas port tweaking only, since we're looking at the same parent cartridge. It would be fun to see one plugging away at barrier targets to see how belt-fed 6.5 materializes, versus 7.62. I would like to see an improvement to the RPD recoil system, but that's another issue. Something like a mini-M60E4 for the Grendel would be sick, with everything scaled-down, and constant recoil, especially since the M60 is a half-bullpup like the FG42 it was inspired from.

[RangerRick]

An RPD/Grendel would probably need gas port tweaking only, since we're looking at the same parent cartridge.

The RPD also has a 3 position gas block to help tune it.

RR

[LRRPF52]

The 7.62x39 uses a rather large gas port diameter since the bore diameter is large, just as the Grendel uses a larger gas port than 5.56. The pressure differences also drive the gas port diameters, but the op-rod is a simple long-stroke system. Since the RPD has a gas regulator plug, that would be easy to manufacture, in addition to a new barrel. Since the RPD uses the 7.62x39 bolt face, one might only need a new barrel if the existing gas regulator facilitates optimum/functional Grendel gas pressure curves. Here's the 1961 Soviet Manual for the RPD for reference:

http://www.scribd.com/doc/31410672/Soviet-RPD-Light-Machine-Gun-Manual-Degtyaryov-1961

The more I look at the RPD, the more it reminds me of the Bren...gas block, regulator, lower receiver, receiver, op-rod, stock...typical Soviet ingenuity.

[LRRPF52]

Holy crap! Did you notice how cheap the DSA RPD's are? They also have full-auto's for LE/DOD agencies.

http://www.dsarms.com/Semi-Auto-762-X-39-RPD-Rifle--RPDCARBINE/productinfo/RPDCARBINE/

One of their parts kits would be great to start with, then get a Grendel barrel. Pull off that PKM flash hider and do something else of course.

http://www.dsarms.com/RPD%20Products/products/205/

[stanc]

Holy crap! Did you notice how cheap the DSA RPD's are?
Sure did. Almost two months ago. :cool:

http://www.65grendel.com/forum/showthread.php?779-The-Ultimate-6.5-Grendel&p=6872&viewfull=1#post6872

Although at the time, I didn't foresee it having any real worth beyond novelty.

[LRRPF52]

You did such a great job of sourcing the picture, that I never clicked on the link to it to see the prices! I've heard of a few guys using cut-down RPD's in SOG in Southeast Asia, as well as the Rhodesian SAS doing the same thing in their conflicts, and it was well-liked for the dismounted commando units due to its lightweight, firepower, and maneuverability. Those are all essential elements to a modern LMG. If it had a quick-change barrel, it would be more viable for the modern era, along with some improvements in the metallurgy, a 1913 rail on the feed tray cover, and the direction DSA is going with it.

I'm having visions of an RPD spitting out Grendel tracers at night on a transition range...

[RangerRick]

Sure did. Almost two months ago. :cool:

http://www.65grendel.com/forum/showthread.php?779-The-Ultimate-6.5-Grendel&p=6872&viewfull=1#post6872

Although at the time, I didn't foresee it having any real worth beyond novelty.

Here is a guy in Florida that builds them even cheaper. http://www.projectguns.com/rpdbuilds.html

Do we want to go full auto are start with semi? The semis have to be modified to shoot from a closed bolt, so it wouldn't be possible to just switch to a full auto lower.

I don't know if semi would satisfy people as a proof of viability.

We can get demiled barrels for $10 if we need a barrel as a pattern for the manufacture of a 6.5.


RR

[bwaites]

As a somewhat disinterested party, I don't think shooting links in semi-auto is going to be impressive to anyone. To be viable, its got to be an auto gun, thats the whole purpose behind the whole link issue.

[stanc]

Paul, some weeks ago you mentioned a European silhouette target, and it had a specific name. I've searched for it without success. Can you please post the name again?

[LRRPF52]

Janter or Jaster. They are different than our E-types in that they are 45cm wide, versus 49.5cm wide. When range-estimating, it makes things very clean with Mils, since a 1 Mil wide Janter is at 450m (450mm/1 Mil=450m), a .5 Mil wide Janter is 950m (450mm/.5=900m), etc. I'm not sure if you'll get much with a google search. The ones in Finland are made from corrugated aluminum plates, attached to radio-controlled pop-up/fall mechanisms often. The E-types we have in the US Army are OD green plastic, with ribs in them for rigidity. The Finns paint the Jasters with camo patterns, and some of the competitions I've been do had sand thrown on them while the paint was still wet...extremely difficult to detect at 400-900m, especially in the noon-sun range of daylight...

[stanc]

Janter or Jaster. I'm not sure if you'll get much with a google search. The ones in Finland are made from corrugated aluminum plates, attached to radio-controlled pop-up/fall mechanisms often.
Didn't find anything at all via google images.

Do they look like the pop-up targets @ 4:30-4:33 in


http://www.youtube.com/watch?v=JA_brhCBRvQ

[LRRPF52]

Nope, those are Russians. The Janter and Jaster targets are a Western European military piece of equipment. I'll look for some photos if I have any and see what I can come up with. They are the pop-up target system used at both FinnSniper and Häyhä every year. I just got an update with pics of this year's Häyhä competition, but there aren't any good pics of the Janter targets, since they put camouflaged uniforms over them, and placed them from 25m-1190m (1300yds).

[LRRPF52]

Here's a good review on the 2007 FinnSniper competition:

http://www.snipercentral.com/forums/viewtopic.php?t=10563

It has several good images of Janter targets.

[longdayjake]

I know that full auto would be most desireable but I am willing to buy a semi-auto cheapy. That said, I have no clue where to get a 6.5 barrel for it.

[stanc]

I know that full auto would be most desireable but I am willing to buy a semi-auto cheapy. That said, I have no clue where to get a 6.5 barrel for it.
It'd have to be custom made. IIRC, RangerRick had a couple of ideas on getting it done.

Now that the steel-cased Wolf FMJ ammo seems near to reality, a 6.5 RPD becomes even more interesting.

[longdayjake]

Now that the steel-cased Wolf FMJ ammo seems near to reality, a 6.5 RPD becomes even more interesting.

That is exactly what I was thinking.

[LRRPF52]

You're going to love this guys...

http://www.army.mil/article/67318/_Ironman__a_game_changer_on_battlefield/

I'm not sure who did it first though, as I have a friend who took a pic of a guy wearing old-school Desert BDU's (chocolate chips from 1980's era/Desert Storm) in Afghanistan with one of these packs, and a hand-held 5.56x45 Minigun. There's also Tyr Tactical...

http://www.tyrtactical.com/products/details/backpacks/mico-light-and-heavy-machine-gunners-assault-pack/

Imagine that with Grendel flowing from it, pushing 144 FMJ's out of a high-pressure-capable LMG that weighs half of the SAW and Mk.48, with a constant recoil mechanism. Release the eeeeeeeeevil....

[stanc]

You're going to love this guys...

http://www.army.mil/article/67318/_Ironman__a_game_changer_on_battlefield/

I'm not sure who did it first though...
The first such pack I remember seeing was that worn by Jesse Ventura in the 1987 movie, Predator.

There was also a photo of a guy with a backpack like that, and an M60 in his hands, on the cover of Machine Gun News in the late '80s or early '90s.

IIRC, my buddy proposed doing it during one of our discussions in the late '70s. Although that idea never went beyond the talking stage, he actually did something somewhat similar when he was an M60 gunner in Vietnam. It was common to have a "starter belt" of about 25-30 rounds loaded in the gun when going on patrol, then when that was fired up during contact, a full 100-rd belt would be loaded. He wasn't content with that SOP, so he scrounged an issue buttpack, fixed a strap to it, and slung it over his right shoulder so that the pack rested on his left hip. Filled with 300 rounds of continuous-linked ammo, it not only balanced the weight of the machine gun, but also gave him a capability for sustained fire unmatched by any other M60 gunner in that war.

Imagine that with Grendel flowing from it, pushing 144 FMJ's out of a high-pressure-capable LMG that weighs half of the SAW and Mk.48, with a constant recoil mechanism. Release the eeeeeeeeevil....
Yeah. Too bad a 6.5 Grendel LMG is only imaginary. :(

[LRRPF52]

That starter-belt SOP continues on well into the current day. We ordered ammo bags specifically made for linked 7.62 from Tactical Tailor, since I had been aware of them back at Lewis. I suggested to our battalion in 82nd to get them before we deployed to OIF1, and we did, but it still didn't provide an on-the-gun ammo feed like the PKM has with the cans.

All good ideas are ideas first...

[longdayjake]

Is it safe to say that nobody is going to try this with a full auto?

[Tony Williams]

Now here's an interesting idea: http://www.thefirearmblog.com/blog/2011/11/10/m249-saw-in-7-62x40mm-wt-300-aac-blk-7-62x39mm-and-7-62x51mm-conversion-kit/


The US Machine Gun Armory have developed a set of kits to convert the MK46 / M249 SAW into a range of 7.62mm calibers including the 7.62x39mm, 7.62x40mm Wilson Tactical, .300 AAC BLK and 7.62x51mm. All that is required is swapping out the top-cover, barrel and a few other parts.


What I'd like to see is them producing a 6.5 mm Grendel version...

[stanc]

Very interesting find, Tony. Do you suppose they use RPD belts for the 7.62x39 conversion?

Contact info, if anybody wants to "lobby" for a 6.5 Grendel kit:

U.S. Machine Gun Armory, LLC.
Suite 415
6300 Sagewood Drive
Park City, UT 84098 USA

sales@machinegunarmory.com

ETA: I'm not sure it matters, though. After thinking about it some more, it doesn't seem likely that a 6.5 Grendel LMG can provide sufficient performance to replace the 7.62 MMG. Even if you compare 20-inch barrels, you're still looking at 150gr @ 2700 fps vs 110gr @ 2600 fps, which makes for a substantial difference in terminal energy.

Plus, the 6.5 bullet will probably have a lower BC, so trajectory wouldn't be as flat, nor effective range as long. And if that isn't bad enough, a 6.5 LMG likely would have a barrel of no more than 16 inches, which would cut velocity down to about 2500 fps.

It seems like it'll be necessary to go with something like the 6.86x46 UIAC in order to have a LMG with 7.62 MMG performance.

[LRRPF52]

I would run at least a 130gr for a machinegun load, and with a half-bullpup design like the M60 or full bullpup, barrel length would not be limited. Even with a conventional design, the 19-20" barrels used on the Mk48 are still maneuverable, while a 20" 7.62 NATO MAG58 is not.

You will need higher pressures to get any 6.86 projectiles to keep up with 7.62 NATO. 6.5mm is the caliber node in short actions when it comes to best trajectory, best wind drift, and lower pressures, with substantial bullet weights.

[stanc]

I would run at least a 130gr for a machinegun load...
Wouldn't that reduce MV and make trajectory even worse?

You will need higher pressures to get any 6.86 projectiles to keep up with 7.62 NATO. 6.5mm is the caliber node in short actions when it comes to best trajectory, best wind drift, and lower pressures, with substantial bullet weights.
:confused: My understanding is that, all other things being equal, it takes higher pressure for a smaller caliber bullet to achieve the same velocity as a bigger caliber, not less.

[JASmith]

If I recall correctly, much of the Grendel military story is based on the 139 grain Scenar bullet and long range performance.

The current interest in bullets of 123 grains and less is largely a result of interest by the hunting community where most of the shots are taken at well under 300 yards.

So, going to 130 grains and slightly really represents a return to the thinking behind the "Grendel as a Universal Military Cartridge."

[stanc]

Hmm. My recollection is that the 123gr Scenar was always the primary basis for comparison, while the 139gr Scenar and the 144gr FMJBT were regarded as too heavy for general military use.

Either way, a 130gr Ball projectile @ 2400 fps just ain't gonna match 7.62 M80 trajectory and energy.

[bwaites]

Hmm. My recollection is that the 123gr Scenar was always the primary basis for comparison, while the 139gr Scenar and the 144gr FMJBT were regarded as too heavy for general military use.

Either way, a 130gr Ball projectile @ 2400 fps just ain't gonna match 7.62 M80 trajectory and energy.

True, but what if the military does what it did with 5.56 ammunition and ups the ante? I keed, I keed.....LOL!! :)

[JASmith]

...My understanding is that, all other things being equal, it takes higher pressure for a smaller caliber bullet to achieve the same velocity as a bigger caliber, not less.
We have to be careful about what we mean by "other things being equal." In the present instance, the sectional density is the operative item to be kept equal simply because that quantity largely determines velocity retention and penetration potential. The .277 bore has right at ten percent more area than does the .264 meaning that a 110 gr .277 bullet will have the same sectional density as a 100 grain .264 bullet.

The smaller bore and same cartridge volume means that a small diameter bullet will see higher pressures longer than would a larger diameter bullet of the same sectional density. This is because the total cartridge and barrel volume is smaller for the smaller diameter bullet.

Restating for clarity: The same total mass of gas in a smaller volume means higher pressures.

[LRRPF52]

An LMG will have a much larger bolt, and won't be limited by AR mag-length COAL. There also won't be a need to save the brass or case for reloading. Basically, you're looking at bolt gun velocity potential, and my friend is getting 2650-2700 fps with 139gr Lapua Scenars out of his Cz527 Grendel, so a 130gr at 2650 should be quite doable.

[stanc]

An LMG will have a much larger bolt, and won't be limited by AR mag-length COAL. Basically, you're looking at bolt gun velocity potential, and my friend is getting 2650-2700 fps with 139gr Lapua Scenars out of his Cz527 Grendel, so a 130gr at 2650 should be quite doable.
Loaded to longer than AR mag length, and to substantially higher than AR pressure? Perhaps.

Although since it's standard practice to have rifles and LMGs in the same caliber, that would rule out conversion of 5.56x45 and 7.62x39 rifles, necessitating development and acquisition of new rifles.

Another point to consider in advocating a 130gr projectile: for the US and NATO, it will need "green" construction (steel tip and copper slug, most likely), while the V4 and Russia would doubtless continue to use steel core. For both, a 130gr bullet would be very long for caliber, longer than the Hornady 120gr GMX (1.4").

Would that present stability problems?

Would it permit a matching Tracer bullet? (Tracers are typically longer than Ball rounds.)

[LRRPF52]

I wouldn't want downrange LMG performance in close-range carbines anyway...makes for disastrous results in the house/CQB, and increases recoil over the current systems unacceptably. Trying to make a cartridge do what 5.56 does within 100m and what 6.5mm Swede does at 700m ain't gonna happen in the same gun with the same load.

Those GMX's are very long indeed. An alloy could address the solids and keep them within length. Tracers only need length for maximum burn distance, and there is plenty of that in 6.5's. I'd be more concerned about throat/barrel burn than anything else really, but the Grendel is very mild on throats in its current state.

[stanc]

I wouldn't want downrange LMG performance in close-range carbines anyway...makes for disastrous results in the house/CQB, and increases recoil over the current systems unacceptably.
IIRC, we've been over this point before. Advocating two different loads -- heavy ball for machine guns and light ball for carbines -- is a nice theory, but the reality is that nearly all the world's armies (China being a notable exception with the 5.8x42) use only one loading for carbines and LMGs.

IMO, any proposal for the use of two loads is a non-starter.

[Tony Williams]

IIRC, we've been over this point before. Advocating two different loads -- heavy ball for machine guns and light ball for carbines -- is a nice theory, but the reality is that nearly all the world's armies (China being a notable exception with the 5.8x42) use only one loading for carbines and LMGs.

IMO, any proposal for the use of two loads is a non-starter.

I agree that a single universal load is very desirable.

Having said that - how often, in the real world of military operations, do you get sections breaking up MG belts to feed rifles, or hastily belting MG ammo from rifle mags? Does it really matter if the belted ammo is different from the rifle ammo? That might be a compromise worth making to obtain the other benefits of one calibre for all rifles and magazine-fed guns.

However, we must also bear in mind that to be worth changing from 7.62mm in belted MGs, the new ammo needs to offer a substantial reduction in weight.

[stanc]

I agree that a single universal load is very desirable.
The main advantage I see is for simplicity in manufacturing.

Having said that - how often, in the real world of military operations, do you get sections breaking up MG belts to feed rifles, or hastily belting MG ammo from rifle mags?
I'd think that it happens very seldom. IIRC, my best friend told me there was one time in Vietnam when he de-linked M60 rounds to feed his XM21 sniper rifle.

Does it really matter if the belted ammo is different from the rifle ammo?
IMO, there's no technical reason to rule out using different weight ball rounds (or for that matter, even having different calibers) for rifle and LMG. After all, rifle ammo comes pre-packed in stripper clips, and LMG ammo in links. But, good luck convincing military leadership to abandon the SOP of having a single load.

[appleseed-kdc]

Well, I just had a reply from machinegunarmory and they said, when asked if they were considering the SAAMI approved 6.5 Grendel for the Multi-caliber m249:-

"we already did the prototypes"


Sounds promising !

[LRRPF52]

A Grendel in the Mk.48 type SAW would be interesting, but they need to cut 12 lbs off that gun to make it maneuverable. I suspect there is already a lot of work being done behind the scenes that none of us will hear about or tell, regarding Grendel in military R&D. It caught the attention of a lot of folks already years ago, so it doesn't surprise me to hear of anyone is testing it. When companies drop the money on R&D, they don't want their results open to every competitor in the industry, as lessons it took them maybe months/years to learn, would be detrimental to their competitive advantage if shared or leaked to others just steps behind them.

[LRRPF52]

Stan & Tony,

Seriously, think about the detrimental effects of a cartridge/projectile/weapon that can deliver substantial downrange energy at 700m, and what it would do when I enter and clear a room, hallway, alley, or courtyard as a member of a combined arms team, with adjacent units within proximity led by officers who are doing multiple breech points for the first time in combat because they never trained on it.

Think about the recoil a 130-140gr class projectile will present for a carbine being fired on SEMI, especially in rapid succession. I don't see a compromise between the requirements for carbines and LMG's to use the same projectile. The SAW in 5.56 is on the wimpy end, so if we are wanting to get rid of the beast M240 in 7.62 for dismounts, it has to launch significant weight projectiles that will pattern well with enough energy out to 800m for human targets, and penetrate light-skinned vehicles at 500m, while blowing through most walls within 100m. That is way too tall an order for a light-recoiling carbine, but perfect for an LMG and DMR.

[RangerRick]

I can tell you this, the Army will never issue a round that will fit in another weapon in the platoon that can't take the pressure.

RR

[LRRPF52]

I can tell you this, the Army will never issue a round that will fit in another weapon in the platoon that can't take the pressure.

RR

That makes a lot of sense, as Joe will find a way to break stuff just by taking it out of the wrapper...

An 80gr SAW projectile in 5.56 wouldn't hurt my feelings though, loaded longer than mag-length.

[stanc]

Stan & Tony,

Seriously, think about the detrimental effects of a cartridge/projectile/weapon that can deliver substantial downrange energy at 700m, and what it would do when I enter and clear a room, hallway, alley, or courtyard as a member of a combined arms team, with adjacent units within proximity led by officers who are doing multiple breech points for the first time in combat because they never trained on it.
I can only note that in WWII, house clearing was done with weapons firing .30 Ball and AP ammo, so perhaps it's more of a theoretical concern than a real problem?

Think about the recoil a 130-140gr class projectile will present for a carbine being fired on SEMI, especially in rapid succession.
IIRC, you have a 6.5 Grendel carbine, and one in 5.56 NATO. Have you run any tests to determine if there is a significant difference in that regard?

I don't see a compromise between the requirements for carbines and LMG's to use the same projectile. The SAW in 5.56 is on the wimpy end, so if we are wanting to get rid of the beast M240 in 7.62 for dismounts, it has to launch significant weight projectiles that will pattern well with enough energy out to 800m for human targets, and penetrate light-skinned vehicles at 500m, while blowing through most walls within 100m. That is way too tall an order for a light-recoiling carbine, but perfect for an LMG and DMR.
Perhaps it is, but how likely is it the US Army (or any other army) would go with two different loadings?

[Tony Williams]

IIRC, you have a 6.5 Grendel carbine, and one in 5.56 NATO. Have you run any tests to determine if there is a significant difference in that regard?

I haven't fired a Grendel, but I have fired (back to back) HK 416 guns in 5.56mm and 6.8mm Rem (which has a very similar recoil impulse to the Grendel). I also fired a 7.62mm HK 417 in the same session. Unfortunately I wasn't allowed to fire them on full-auto but I did get a good impression of how the recoil compared (that was why I was testing them).

If you calculate the recoil energy, the 6.8mm sits half-way between the 5.56mm and 7.62mm in similar guns, but since the HK 417 is noticeably heavier than the HK 416 (thereby reducing the recoil) I would have expected the recoil of the 6.8mm to feel closer to the 7.62mm than the 5.56mm. In fact, the opposite was true - the kick of the 6.8mm felt much closer to the 5.56mm, the recoil of the 7.62mm was a much bigger step up.

This ties in with the MURG tests which compared 5.56mm with 6.8mm and concluded that there was no difference in the practical rate of aimed fire or the hit probability.

This suggests to me that there is a kind of recoil threshold below which most people can control the gun, but above which they can't. The 6.8mm Rem falls below the threshold (therefore the 6.5mm Gren should as well), the 7.62mm is clearly above it.

[stanc]

I haven't fired a Grendel, but I have fired (back to back) HK 416 guns in 5.56mm and 6.8mm Rem (which has a very similar recoil impulse to the Grendel). I also fired a 7.62mm HK 417 in the same session. Unfortunately I wasn't allowed to fire them on full-auto but I did get a good impression of how the recoil compared (that was why I was testing them).

If you calculate the recoil energy, the 6.8mm sits half-way between the 5.56mm and 7.62mm in similar guns, but since the HK 417 is noticeably heavier than the HK 416 (thereby reducing the recoil) I would have expected the recoil of the 6.8mm to feel closer to the 7.62mm than the 5.56mm. In fact, the opposite was true - the kick of the 6.8mm felt much closer to the 5.56mm, the recoil of the 7.62mm was a much bigger step up.
That's what the guys on 68forums have said. I don't understand how the calculated recoil can be so much greater, but perceived as not significantly different.

Interestingly, there's a contrary view at the end of this video; the felt recoil of 6.8 SPC is rated as equal to that of 7.62x51.


http://www.youtube.com/watch?v=nKy3930MO2k

This ties in with the MURG tests which compared 5.56mm with 6.8mm and concluded that there was no difference in the practical rate of aimed fire or the hit probability.

This suggests to me that there is a kind of recoil threshold below which most people can control the gun, but above which they can't.
That sounds plausible.

[stanc]

You're going to love this guys...

http://www.army.mil/article/67318/_Ironman__a_game_changer_on_battlefield/

I'm not sure who did it first though....
Maybe Gene Stoner? Check 4:34 in this late-1950s film:


http://www.youtube.com/watch?v=iTeMU61qKGY

It took only half a century for the idea to be implemented...

[LRRPF52]

I will have to do your cinder block test with the 100gr NBT's at 2700fps MV to see what happens, or maybe find another 100gr bullet that closely resembles an FMJ or M855A1. Maybe a Barnes 100gr TSX?

[stanc]

I don't know how penetration capability of a NBT or TTSX might differ from that of an FMJ. But, a 100gr FMJ is available.

http://www.midwayusa.com/product/142377/lapua-bullets-264-caliber-65mm-264-diameter-100-grain-full-metal-jacket-box-of-100

[RangerRick]

Maybe Gene Stoner? Check 4:34 in this late-1950s film:

It took only half a century for the idea to be implemented...

I like how he turns around and sweeps the cameraman with a big grin! LOL!

RR

[LRRPF52]

So I walked up to DSA's booth today at SHOT, looking to float the 6.5 Grendel/RPD conversion, when they told me to go look at the gun on the counter. It was chambered in 6.8 SPC, with plenty of rounds in the non-disintegrating links from 7.62x39. That would provide some advantage over 7.62x39, but I think we can all agree that the Grendel would give the gun a true 800m beaten zone capability that is superior to the 6.8 SPC, and would provide better penetration within 500m on barriers with higher sectional density bullets too.

I spent some time talking with one of their engineers about the project, and ironed out what he needs to make it happen. Since the RPD has 4 gas settings already on the gas block/regulator, we could use a large gas port on a test barrel and mitigate with the existing block as-is, since their is a wide spread in ga sport diameters in the regulator. Grendel fits in 7.62x39 links already as we have seen, so all we need is a barrel and we're on the way. I have to tell you... that RPD with a 100rd SAW nutsack and the 6.8 linked is really lightweight. It would make an awesome LMG to have everything in that weight & length profile, since the gun is something like 14lbs. The bolt will take high pressures too.

[stanc]

So I walked up to DSA's booth today at SHOT, looking to float the 6.5 Grendel/RPD conversion...

I spent some time talking with one of their engineers about the project, and ironed out what he needs to make it happen. Since the RPD has 4 gas settings already on the gas block/regulator, we could use a large gas port on a test barrel and mitigate with the existing block as-is, since their is a wide spread in ga sport diameters in the regulator. Grendel fits in 7.62x39 links already as we have seen, so all we need is a barrel and we're on the way.
Did he give you any feeling that DSA might pursue this?

[LRRPF52]

Did he give you any feeling that DSA might pursue this?

If I push it, he seemed open to doing it actually. He would need gauges, a reamer, NO-GO/GO, etc.

I talked with another major industry figure and his son about the concept. I think the important thing to push is how this is a major game-changer for small arms development when it happens, from a historical perspective. Getting rid of the 5.56 LMG and 7.62 GPMG in one system that is half the weight of most belt-fed guns is truly a game-changer.

[stanc]

If I push it, he seemed open to doing it actually. He would need gauges, a reamer, NO-GO/GO, etc.
So, are you gonna push it?

[LRRPF52]

I learned recently that there is an 07 FFL holder in my area who does modifications on existing machinegun designs, to include an HK fire control group/grip on SAW's, Mk46's, Mk48's, etc., as well as caliber conversions on them. I think they would be the best route to take with this project.

I was looking at old pics of guys in SOG who carried the RPD for its lightweight, compactness, and firepower.

http://www.modernforces.com/img/new_site/2011_brightlight_7.jpg

[stanc]

I learned recently that there is an 07 FFL holder in my area who does modifications on existing machinegun designs, to include an HK fire control group/grip on SAW's, Mk46's, Mk48's, etc., as well as caliber conversions on them. I think they would be the best route to take with this project, compactness, and firepower.
Sounds promising. I wonder if they can give a cost estimate?

[LRRPF52]

I have to tell you how impressed I am with the handling and balance of the RPD. It's been a while since I played with one, and it is very slim, light, and about perfect for an LMG.

I also saw something really cool from Tango Down...an AK quick barrel change system with an interrupted thread system, and a detent protruding out of the barrel trunnion. It would be cool to use that design on the RPD so it has a barrel change feature.

[LRRPF52]

Check this out:


http://www.youtube.com/watch?v=yL2Wd-nuiZ4&feature=player_embedded

[bwaites]

Interesting. Sounds suppressed, intergral suppressor maybe? But that's a lot of rounds to carry and expend! Very nice.

[BjornF16]

Check this out:


http://www.youtube.com/watch?v=yL2Wd-nuiZ4&feature=player_embedded

Did we lose the video file?

[bwaites]

Did we lose the video file?

Still works for me.

[BjornF16]

OS X update...had to reboot. All works now...LOL. Thought the spammers had struck again...

[stanc]

Interesting. Sounds suppressed, intergral suppressor maybe?
Nah, just poor sound reproduction. That's quite common in videos such as this.

I'd like to see the negative characteristics of these back pack systems. They never show us that.

[txgunner00]

I'd like to see the negative characteristics of these back pack systems. They never show us that.

+1 I bet it's heavy as hell.

Cool concept though.

[HANKA]

I coulda sworn there's a video of Gene Stoner himself, from the '50s, wearing an ammo backpack and firing an LMG in exactly the same way. OK, hell, gimme a sec to Google it. . . . OK, got it.

Link: http://www.youtube.com/watch?feature=player_embedded&v=CVKHBQ9YpNs . Start at the 6:00 mark.

John