Grendel LMG

[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.)


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.

[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.

[stanc]

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.

Concur. IMO, the only real question mark is the possible effect of the different case taper on fitting in, and feeding from, links designed for 7.62x39.

[stanc]

I wonder if Bill A would be interested in this?

Maybe. If it looks like it might work.

[stanc]

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.

<sigh> In due time, Joe. In due time. We're not anywhere near there, yet. Right now we're just acquiring information to examine the feasibility of this project.

[JASmith]

<sigh>

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

[stanc]

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?

P.S. I forgot to note that, while I would like to see it done at 100, 200 and 300 yards, I leave the final decision to you. After all, it's you who'll be doing the tests. I shall be happy to see the results regardless of what distance(s) you opt to use.

[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?