Optimized Caliber

[stanc]

The 2011 NDIA Small Arms presentations are now online.

Jim Schatz makes a proposal very similar to that given by Tony Williams in 2010.

http://www.dtic.mil/ndia/2011smallarms/WednesdayAmmo11456Schatz.pdf

Warning: 7 MB file size

[stanc]

Here are the specs I would like to see, and I guarantee that soldiers and small unit leaders would welcome:

1) System replaces M249 SAW and M240 machineguns for dismounts
2) Cartridge offers ballistic improvements over 5.56 NATO in trajectory, wind drift and penetration of mud brick, cinder block, and vehicles at 500m
3) Cartridge weighs less than 7.62 NATO, allowing at least a 20% threshold increase in ammunition carrying capacity in linked form, with an objective of 30%...without losing any elevation trajectory or penetration of equal mediums at 700m

How about 37% lighter than 7.62 NATO, and 8% lighter than 6.8 SPC or 6.5 Grendel, with flatter trajectory than any of those?

For an optimized military cartridge, 6x41 looks really good to me. Not only for a new LMG, but also for conversion of 5.56 rifles.

http://68forums.com/forums/showthread.php?15855-6x41&p=154811&viewfull=1#post154811

[BluntForceTrauma]

Stan, I wouldn't cry too much over such a cartridge, but the specs posted in the link would need to be verified in the real world. Every wildcatter's fantasy has amazing performance until independently verified under conditions and configurations which may not show it quite in the light the wildcatter would hope.

John

[bwaites]

Hmmm....Same case capacity as the 6.8, but shooting a 95 grain bullet at velocities that are similar to the AR Turbo, which has more case capacity. I'm not convinced its going to work!

[stanc]

7x50mm

Interesting Israeli 7mm "intermediate" cartridge discovered.

http://iaaforum.org/forum3/viewtopic.php?f=8&t=11781

[stanc]

Thread on Tony Williams' forum about using a KelTec bullpup rifle to test and evaluate the 6.5/8/800 concept:

http://forums.delphiforums.com/n/mb/message.asp?webtag=autogun&msg=4861.1

[LRRPF52]

That's funny, because I was just thinking about the Universal Infantry Cartridge Thread and I walked away thinking that the 800m and CQB requirement could be met with a bullpup with .260 Rem or 6.5x47 Lapua ballistics. If you used a polygonal rifled barrel, you could maybe increase the barrel life. Since the Grendel already will bite the heels of .260 Rem out of a bolt gun, I would lean towards the Grendel case with longer mag COAL, meaning a new magazine design entirely. The bullpup would also need a larger bolt geometry to take the pressures, since we are talking about a higher pressure cartridge no matter how you look at it. To get the pressures more moderate, you need to increase case capacity and that means larger mags, less mag capacity, etc.

With the magazine in the rear of the weapon, you do face certain prone profile limitations that aren't ideal, especially if you're using a magazine with more capacity than 20rds. I don't think the mag change issue is a huge deal, and ejection is solved with the forward eject system prototyped by the Soviets that everyone is copying now. The real hurdles that would need to be overcome would be ergonomic interface as to mag release and bolt catch/bolt hold-open with the firing hand.

The Tavor has addressed the selector control, but it has a mag release that requires two hands, and the bolt stop is at the toe of the butt of all places. I like bullpups, but have yet to see a real viable platform with the features I like, to include the above ergonomic interface devices that are standard on the AR.

To the layman, we are basically re-visiting the EM-2/.280 Enfield.

[txgunner00]

Interesting but the 2900 does seem a bit optimistic.

[stanc]

Interesting but the 2900 does seem a bit optimistic.

I think MV of the 6x41 has since been revised down to 2800 fps.

[LRRPF52]

That is still good velocity. There aren't any military-grade projectiles for it, but it would be another wildcat for AR shooters. The 6mm AR requires only sizing down, while the 6.8 needs to be trimmed for length, then sized, has more powder, and more bullet selection for competitors since you can use longer VLD-types without taking case capacity, and still mag-length load.

6mm doesn't offer enough over 5.56 for 55gr-70gr performance out of an AR with FMJ pills, and doesn't have the retained energy a lot of people expect out of an LMG for 500-800m terminal performance, so that is why I lean to the idea that a 6.5mm in the 130-140gr class is ideal for a Multi-role LMG.

[stanc]

6mm...doesn't have the retained energy a lot of people expect out of an LMG for 500-800m terminal performance, so that is why I lean to the idea that a 6.5mm in the 130-140gr class is ideal for a Multi-role LMG.

You may be right, but I don't see how you're going to get practical "green" bullets heavier than ~120gr.

And in order to attract attention of anybody in the military, won't it be necessary to demonstrate that a 6.5 LMG actually can deliver the required performance?

[LRRPF52]

I would actually look more seriously at a 130gr projectile minimum for an LMG, if not 140gr like the x55 Swede used. Since COAL isn't an issue for keeping within an AR15 mag length/receiver, and you can design the bolt from the ground up as a high-strength component, and you won't be concerned with reloading the brass, a 130-140gr LMG military projectile is more than feasible, and can be launched at 2600-2700fps with the right powder specific to that loading after the RDT&E is done on it.

Then drop that into a constant-recoil LMG, and you have game day as far as capability is concerned. A 2600fps 140gr 6.5mm FMJ or MP projectile will start to out-gas a 147gr M80 at 300yds, even though it starts out 200fps slower. The 144 FMJ is another option that really smokes 7.62 at distances where GPMG's really come into play.

It's definitely worth pursuing in my book.

[stanc]

I agree it's worth pursuing. It's just that, as presented, the idea raises a couple of questions:

You say that "a 130-140gr LMG military projectile is more than feasible." On what basis do you make that claim? It looks to me like the steel/copper and steel/steel construction being used in American, European, and Scandinavian "green" bullets will result in a ~120gr 6.5mm bullet the same length as the 120gr GMX (1.4"). That makes for a 5.3 L/D ratio. For a 130-140gr it would increase to the 5.8-6.8 range. Is that truly feasible?

AFAIK, the "constant recoil" principle has only been applied to 5.56mm machine guns. What evidence is there to show it is viable for more powerful cartridges, such as your 6.5 Grendel +P+ load? Do you know of any constant recoil 7.62mm machine guns?

ETA: The heaviest copper solid spitzer boattail I could find is a 128gr GSC. Note the very fast twist rifling required to stabilize the 1.51" projectile.

http://www.gsgroup.co.za/264128SP060.html

[LRRPF52]

The constant recoil principle spans several different designs, and a wide caliber range. It is not beholden to any specific caliber, just as there are different operating systems, and recoil mitigation devices covering small bore up to artillery pieces. The Suomi Kp31 9mm SMG uses constant recoil. The 7.92x33mm German MP44/Stg44 uses constant recoil as well. I believe they are the first two shoulder-fired infantry weapons to have ever used it.

The 130-140gr weights are based on traditional bullet designs in FMJ's. A military looking for an affordable cartridge will not hold itself to environmental protection guises disguising economic warfare from within, as I suspect the "green" ammunition push to be, modeled after the restrictions on lead for fowl hunting, with no scientific basis for environmental protection, and a true agenda to disarm populaces via incrementalism. Since I don't see them fielding a "green" M80 any time soon, we needn't operate under the limitation that any future LMG cartridge must be "green". It would bankrupt current ammo budgets, which may be the goal of the EPA useful idiots in the hands of their Marxist overlords...

The 6.5x55 Swede has proven itself not only in decades of warfare, but across the game spectrum from medium-sized critters to large African species. An LMG duplicating 6.5x55 Swede ballistics, which has already been done actually if you look at the Swedish BAR's, is a proven system already from the muzzle-to-target standpoint. It just needs the platform built and fielded to an Army that prioritizes logic in its weapons procurement philosophy, not corruption and cronyism, so that pretty much rules out the US if business is as-usual in the Pentagon.

[stanc]

The 130-140gr weights are based on traditional bullet designs in FMJ's. Since I don't see them fielding a "green" M80 any time soon, we needn't operate under the limitation that any future LMG cartridge must be "green".

M80A1 is being developed, and IIRC fielding is expected to begin in late 2012.

As I recall, "green" ammo is already in service in one or more Scandinavian countries, as well as the USA, and being planned for in the UK and Europe. IMO, to ignore the clear trend is, in the absence of evidence to the contrary, wishful thinking.

Also, where economics may prevail over environmental concerns, such as in the less affluent nations of Eastern Europe, the typical military bullet has a steel core. That type of construction results in a projectile just as long as a "green" bullet.

If your 6.5 LMG concept depends upon the use of lead-core heavy bullets in order to be viable, it seems to me you're severely reducing the chances of success.