Optimized Caliber

[LRRPF52]

Here's an article about the new carbine being sought. No mention of a new cartridge. I wish it were different; I'd love to see something like an HK416 in 6.5 Grendel adopted.

http://www.military.com/news/article/gun...ompli.html

I can't stand the HK416. It handles horribly compared to a DI M4, even when suppressed. The M4A1 SOMPOD Block II is the way to go, in 5.56 NATO. The main improvements that the M4 needs is removal of that Gypsy witch doctor abortion 3rd BURST mechanism, and installation of a polished A1 trigger and hammer FCG, followed by a mid-length or rifle-length free-float handguard, plus FDE Cerakote finish on all the metal parts. This is what SOCOM is doing already (SOCOM always had M4A1's with the A1 trigger mechanism). Free-floating helps with heat dissipation, no loss of zero with accessories, weapon longevity since dynamic tension on the handguard no longer induces stress on the barrel extension with high temps, and of course, accuracy.

The caliber needs to stay the same. 5.56 is an awesome cartridge for the Rifleman, Grenadier, Fire Team Leader, Squad Leader, RTO, PL, Scout/Observer, Designated Marksman with 77gr Mk262, Ammo Bearer, Assistant Machine-Gunner, Forward Observer, Combat Medic, Assaulter, Combat Engineer, and any other dismounted duty position frequently placed in the realm of Light Infantry engagements. Any suggestion that these duty positions should be sapped with heavier and less ammunition would not be met well with the troops, and would reduce the number of bounding overwatch cycles that a dismounted unit could conduct before needing to be re-supplied or relieved after reaching critically-low ammunition loads.

[txgunner00]

... The main improvements that the M4 needs is removal of that Gypsy witch doctor abortion 3rd BURST mechanism, and installation of a polished A1 trigger and hammer FCG, f...

LOL. That's a good way to describe it. I agree.

[LRRPF52]

The Army has already started removing the 3rd BURST mechs and installing AUTO triggers. Whoever instituted the 3rd BURST mechanims on the M16A2 needs to be flogged with rusty MILES gear harnesses.

[txgunner00]

MILES. yuck :p

Those engineers should be thrown to the dogs.

[LRRPF52]

Back to the new MultiRole LMG concept. It has been mentioned in this thread that a 130gr Solid has already been made, namely the Barnes 130gr. They have also come out with a Barnes 127gr LRX long-range hunting bullet. There are no practical limitations on a "green" projectile of already-in-use bullet lengths that are viable in the Grendel.

There is also a new member here chambering a 1919A4 Browning in Grendel, and is using disintegrating links made of nylon:

http://www.65grendel.com/forum/showthrea...#post27594

I was thinking you could take existing M27 links and run them through an expander mandrel after heating them, so they open up to the Grendel case body for a prototype LMG.

I can't wait to see the actual constant recoil principle LMG spitting 130-140gr Grendel loads out next to a 7.62 GPMG, and beating it for wind deflection and penetration. This is a vision I've had for years.

[stanc]

Jordanian Secret Service has purchased 6.8 SPC PDW's from LWRC, and there is a totally different lower/upper receiver set on that PDW.

To infer that the 6.8 is gaining widespread military adoption because of the Beduin King's body guard service in Jordan is a bit of a stretch.

There is zero reason to deviate from 5.56 in a carbine for military use. The biggest demand is in quality range time, which is not currently supported by most of the military. Adoption of a new caliber for carbines would only exacerbate the current situation.

I don't see 6.8 being adopted by any organization in the DOD. Even SOCOM, I'm sure, would stick with 5.56, if only for logistical reasons.

If any entity is actually planning to adopt 6.8, as the LWRC guys have intimated, I'd bet it's the Coast Guard. The USCG previously demonstrated independence in such matters by adopting .40 S&W for their standard pistol caliber. They may well be planning to do so again for their rifle cartridge.

Back to the new MultiRole LMG concept. It has been mentioned in this thread that a 130gr Solid has already been made, namely the Barnes 130gr. They have also come out with a Barnes 127gr LRX long-range hunting bullet. There are no practical limitations on a "green" projectile of already-in-use bullet lengths that are viable in the Grendel.

Forgive me, but I remain skeptical. The 130gr TSX is 100% copper, while "green" military ball projectiles with steel/copper or steel/steel cores would be significantly lighter. The same is true of conventional steel-core w/lead sheath construction, as shown by the Swedish AP bullet, which weighs a tad more than 110gr.

If you want me to buy into the idea of 130-140gr "green" or steel core, military ball, you'll have to provide much better evidence.

There is also a new member here chambering a 1919A4 Browning in Grendel, and is using disintegrating links made of nylon:

http://www.65grendel.com/forum/showthrea...#post27594

Yeah, that looks interesting.

I was thinking you could take existing M27 links and run them through an expander mandrel after heating them, so they open up to the Grendel case body for a prototype LMG.

So try it and let us know if it works.

I can't wait to see the actual constant recoil principle LMG spitting 130-140gr Grendel loads out next to a 7.62 GPMG, and beating it for wind deflection and penetration. This is a vision I've had for years.

I'd like to see it, too.

[Schwag173]

Schwag, have you played much with the HK416? I've seen and handled them several times. While the idea seems great, the actual shooting experience was very disappointing according to friends whom I trust in such things.

Admittedly, no. That's why I was careful to add the word "like." I can see why, in military circles, a piston-AR would viewed as an improvement over the DI design. I'm with you on the wonderful balance and handling qualities of the original.


My aforementioned friend said it best; "The average Joe (grunt) just wants a rifle that will go bang every time he pulls the trigger. Instead, the Army keeps searching (in vain) for the ultra-space-age technological masterpiece."

[LRRPF52]

Admittedly, no. That's why I was careful to add the word "like." I can see why, in military circles, a piston-AR would viewed as an improvement over the DI design. I'm with you on the wonderful balance and handling qualities of the original.


My aforementioned friend said it best; "The average Joe (grunt) just wants a rifle that will go bang every time he pulls the trigger. Instead, the Army keeps searching (in vain) for the ultra-space-age technological masterpiece."

The funny thing is that one of the biggest factors in reliability with the AR15 family of weapons lies right in the soldier's hands and individual control: proper lubrication. The military and industry has already provided him with an extremely reliable weapon, with great ammunition and reliable magazines. If he would just keep the bolt carrier wet, it will run like a champ-better than AK's and other assault rifles, in my experience.

[Schwag173]

The funny thing is that one of the biggest factors in reliability with the AR15 family of weapons lies right in the soldier's hands and individual control: proper lubrication. The military and industry has already provided him with an extremely reliable weapon, with great ammunition and reliable magazines. If he would just keep the bolt carrier wet, it will run like a champ-better than AK's and other assault rifles, in my experience.

Personally, I agree that DI is fine the way it is. But ... there's that rare scenario now and again so I at least tolerate the (military) interest in piston guns. I own nothing but DI and have had many a debate with a co-worker that is excessively proud of his piston guns. I got that former Marine to bow his head in admission that he never had a DI gun stoppage the entire time he was in the Corps. Had him on that one.

[LRRPF52]

There's a lot to be said for a design that keeps all the moving parts isolated from external debris as much as practically possible. Once you locate critical components outside and exposed to fine & large sand particles, you're asking for the system to cough. Not to say that the DI system won't choke in the worst of conditions, but I feel that it prolongs the inevitable more than an op-rod driven gun.

Out of 10 years in the Army spending most of that time either in the field or forward-deployed, I had very few malfs with my issued M16A1's, M16A2's, M4's, and M4A1's. The very few malfs that I did have involved one of these scenarios:

1) A 30rd magazine that was so old, the aluminum had turned orange, with the spine splitting and feed lips all jacked up
2) No lubrication on a recently command inspection-stripped dry M4
3) Mega dust storm where the weather front covered an area spanning from Eastern Turkey to Northeastern Egypt, and swept eastward through the Levant, Mesopotamia, and Arabian Peninsula like a massive hurricane that hits the Eastern US Seaboard-only with dust replacing the rain. Not even our M24's or breacher shotguns could chamber a round in that environment, so good luck with any self-loader.

[txgunner00]

Same here on causes of malfunctions in my experience. 90% magazine related, 9% lubrication related, 1% other.

Maybe in the future piston will be the way to go but there are presently too many unknowns for my taste.

[stanc]

Back to the new MultiRole LMG concept.

I was thinking you could take existing M27 links and run them through an expander mandrel after heating them, so they open up to the Grendel case body for a prototype LMG.

I just remembered something. You may wish to check with Bill A about that idea. Perhaps 6-8 years ago, he posted a photo of a few rounds of 6.5 Grendel belted together in M27 links. He never said if he altered the links to increase the loop diameter, or if he just forced the rounds in.

But, the question isn't if the 6.5 round can fit into such a link. That's already been demonstrated. Bill A did it with 5.56mm M27 links, and I did it with 6mm SAW links (which I recently gave to Bill W), which are identical to M27 links except for larger loop diameter and longer indexing tabs.

The real issue is compatibility with the feed mechanism. With 5.56, the front feed pawl pushes against the cartridge shoulder, and the cartridge stop also engages the shoulder. With 6.5, there appears to be too little case shoulder ahead of the link for that to work. See attached photo.

[LRRPF52]

I was thinking about the same thing when looking at the Grendel case and the longer shoulder position of the 5.56 NATO case, especially when considering the feed pawls. The question isn't about getting the cartridge aligned properly, but if there is enough traction in the feed mechanism to purchase the cartridge on enough surface area to pull the Grendel cases through the feed mechanism.

Thinking back on the underside of the feed tray cover, where the heart of the belt-fed system lies, there are 2 feed pawls IIRC. One pulls the area ahead of the link, and one pulls on the base of the cartidge. Your point makes a lot more sense now, as I was thinking that you were saying that a Grendel link couldn't be made based on loop diameter or something.

One possible solution to this could be having the forward feed pawl a little longer and contoured so that it pulls the cartridge neck. That would be an easy solution, as long as it doesn't interfere with the ability to strip the cartridge from the links and drive it forward into the feed ramp that's on the bottom of the feed tray.

[LRRPF52]

Another thing about the manner in which the feed tray mechanism cycles is that when the bolt carrier group drives forward, the cam rides inside of the curved arm that moves the feed pawls, which are under spring tension so they can ride over the cartridge and purchase the next one.

After the fired cartridge's gas begins to operate the action, the op-rod and bolt carrier move rearward, which drives the cam back in the track to pull the next cartidge into the feed slot on the feed tray, so it looks like the mechanism would likely function even without modification using the Grendel case. The main issue that might come into a play is a completely new feed tray cover with a higher clearance for the larger cases, but using the same subcomponents.

[txgunner00]

I would think it could be done without too much modification. Maybe a different feed tray (or just the stop) to fit the profile of the Grendel case and different pawls, possibly just the front pawl can grab the neck instead of the case body.

[stanc]

On the old forum, somebody else suggested having the front feed pawl push against the case neck. I don't know whether or not that's a viable option, but I've never heard of any machine gun that does it.

Back in 2006, a gunsmith friend took some measurements on an M249. The front and rear feed pawls are 0.241" in width, with spacing as shown on the attached picture.

The feed tray would require a new cartridge stop, reconfigured as shown. The left side of the stop would need to be shifted ~0.03" to the right to allow for correct alignment of the fatter cartridge with the feed slot. And note that even changing the lower left from a 45-degree bevel to a 90-degree corner, contact with the case shoulder looks rather iffy.

[stanc]

I was browsing Tony Williams' forum tonight. They, too, have had endless discussions/debates about designing a cartridge that could replace 7.62 NATO. Apparently they've settled on what they call a 6.5/8/800 (6.5mm 8-gram bullet @ 800 m/sec).

One member suggests using an AR-10 in 6.5 Creedmore as a proof-of-concept demonstrator.

...to quickly evaluate the 6.5/8/800 concept from an assault rifle, then an AR10 clone with a 16" bbl like the L129 (with select fire option) chambered in 6.5mm Creedmoor might be a good start IMO.

http://forums.delphiforums.com/autogun/m...msg=5041.3

...a quick and cheap capability demonstrator one could use to help prove and sell the concept of 6.5/8/800 from a performance standpoint. It would demonstrate the superior exterior ballistics, demonstrate terminal ballistics, and demonstrate controllability of such a cartridge.

It would also be easy to convert a Mk48 LMG over to 6.5mm Creedmoor or 6.5x47mm Lapua to demonstrate the capability of the 6.5/8/800 concept to replace 7.62mm NATO in the machinegun role.

I may be wrong but I think the military brass may need to be sold on the need for, and the capabilities of, a 6.5/8/800 type cartridge before they can be sold an actual idealized 6.5/8/800 cartridge.

http://forums.delphiforums.com/autogun/m...msg=5041.5

Unfortunately, nobody seems interested in getting a gun and actually shooting it to see if reality matches their theory.



Another thread of possible interest:

I have been involved in a fairly lengthy industry discussion about medium caliber military cartridges. Now that everyone has access to basic ballistic calculators, there is some doubt about whether our ideal 6.5 mm to 7 mm cartridge would offer a significant enough weight saving versus 7.62 mm to justify adoption. In order to achieve a flat trajectory and to match 7.62 mm at 1,000 metres, it is argued that we would need a cartridge that's quite close to the M80 in size, volume and weight.

Cris Murray's 6.86 mm UIAC is an example of the problem: clearly a very good cartridge. But the weight saving isn't even 10%.

http://forums.delphiforums.com/autogun/m...msg=5023.1

[LRRPF52]

They have correctly identified one of the problems with the 7.62 NATO-based cartridges: Weight/size

I want to get rid of the whole T65/M80 case because of the weight/size penalty it brings with it. It also is not a good case for a high-volume military weapon for a 6.5mm because of over-bore and throat erosion, although some of that can be dealt with using modern metallurgy.

This further steers us to the shorter .445" case head diameter, made of strong brass capable of higher pressures, with a shorter overall length. We don't need a case volume of 44-50grs to beat the 7.62 NATO when pushing 6.5mm bullets either.

I really think a 130gr Grendel is the way to go.

[stanc]

I'm not sure how significant this is, but note the calibers:

SWEAT Course (Soldier Weapon, Equipment, and Test)
Sponsored By JSSAP

Page 15

Determine the Ballistics Protection/Bullet Traps for Each Station
•
Ballistic protection plan designed to preserve overall lifetime of course and keep a low total of cost ownership
•
Design Considerations
•
Create safe and realistic environment
•
Ammunition
•
9mm
•
5.56 (M855A1 in Phase II)
•
5.7mm
•
6.5mm
•
6.8mm
•
7.62
•
Maintenance life-cycle cost
•
Durability

http://www.dtic.mil/ndia/2011smallarms/T...Wilson.pdf

[Tony Williams]

I've been photoshopping again

Some thoughts on the options for a GPC (General Purpose Cartridge) which could replace the 7.62x51 in portable small arms carried by dismounted infantry with substantial reductions in weight and recoil (and could also replace the 5.56mm in the infantry squad, although that would stick around for a long time in non-infantry applications).

I start with the assumption that the ideal GPC cannot be accommodated in the AR-15 platform. The Grendel is by far the best attempt to do so but, as is being discussed on another thread on this forum, the case width limits the maximum safe pressure to around 50,000 psi, which I suspect isn't quite enough to extract the performance required to replace the 7.62mm. Particularly when the US Army's preference for lead-free bullets is taken into account (longer bullets = less room for propellant). So all of the proposals below exceed the overall length of the 5.56x45.

The first three on the left are based on the 6.8mm Rem only with the case extended slightly to 45mm and (more importantly) the overall length allowed to grow a lot more to use higher-BC bullets. The three versions show 6.35mm, 6.5mm and 6.8mm calibres. These were chosen because the ARDEC calibre survey tested cartridges in 6.35mm and 6.8mm (but not 6.5mm) and concluded that these two were both better than 5.56mm, 6mm or 7.62mm.

The next three (in the same calibres) are based on the Grendel, only with the case extended to 42mm. The longer OAL would ensure that they could not be chambered in modified AR-15 actions, so could be loaded to higher pressures. Maybe this could be designated something like 6.5GM (Grendel Maximum)? With the increasing availability of commercial rifles based on the AR-10 action, this could find plenty of good homes as a big brother to the Grendel (and being a bullpup supporter, I'd love to see one of these in a Kel-Tec RFB!). There is obviously room to extend the OAL to accommodate lead-free bullets. The aim would be to match the performance of the 6.5 Grendel in 24 inch barrels (in metric round figures, 8g at 800m/s, or 123 grains at 2,620 fps) only with longer, lead-free bullets in shorter barrels (20 inch, with decent performance maintained from carbine barrels).

The final cartridge is the 7.62x51 for comparison.

The cartridges shown in the pic are purely indicative and the designs would doubtless be amended by people who know more about the technicalities than I do.

Comments?