When you look at the soldier’s load, ammo is a natural place to consider weight reductions. Less weight means more ammo. To deal with ammo weight, we can make the bullets smaller, or change their composition. We’ve tried Caseless Ammo, and that proved to have some significant technical challenges. What if we kept the case, but made it from something else?
Enter the LSAT project.
The idea behind LSAT was to create lighter cartridges using polymer cases and telescoped1 cartridge construction, and compare those to using caseless ammo based on the G-11 project. Of course, polymer isn’t brass, and this presents some design challenges. With a brass case, you can make a sturdy rim2 that an extractor claw can grab. You can then pull the case, spent or live, out of the chamber. This doesn’t work for polymer cases. A polymer rim of similar design isn’t strong enough for an extractor claw to pull the round out. You can only push the polymer case, which makes ejection a challenge.
To deal with this problem, the LSAT light machine gun uses a swinging chamber. When the chamber swings down to feed a round, the previous round is pushed forward into the ejection chute. The chamber then swings up to interface with the barrel for firing.
The focus of LSAT was a Light Machine Gun first setup, since the current US Army LMG, the M249, is considerably heavier than an M4. There’s more weight savings to be had there. The end result was a weapon prototype that weighed 9.4 lbs for the polymer-cased telescoped ammo version3. The version firing caseless ammo weighed a little more because of the need for extra components to provide an adequate chamber seal. Polymer-cased telescoped ammo is 40% lighter and takes up 12% less volume than conventional brass-cased ammo, so a belt of 100 rounds of 5.56 mm LSAT ammo weighs about 2 pounds, rather than the roughly 3.3 lbs for a 100 round belt of 5.56 mm NATO.
Let’s briefly talk about the LSAT rifle before getting into some analysis. The LSAT rifle is much less further along designwise than the LSAT LMG. Much of this is due to the fact that the US Army’s existing rifle, the M4, is already really lightweight. It’s an excellent weapon, and weight savings from ammo changes will be less noticeable with a 30 round magazine than with a 100 or 200 round belt. Further weight savings here are likely going to require materials changes.
Recently, the LSAT program started looking at the development of 6.5 mm cased telescoped ammunition, and weapons to fire them.
And now for the breakdown. First, I like the idea of continuing research into small arms development. And I like the idea of trying to keep it evolutionary rather than trying to force a revolution like with Project SPIW or the OICW. I like the LSAT LMG and the 5.56 mm LSAT round best. I’m a big fan of weight reduction, and the weight reduction in both weapon and ammo weight are big wins for the infantryman. I also like that combination for really only having one variable being played with. We’re still using the same 5.56 mm rounds, with the 5.56 mm bullets that we know, but we’re trying to use new materials to reduce the weight burden.
I’m also fine with the 5.56 mm LSAT rifle being put on the back burner. Weight savings from lighter bullets is less attractive here because we’re dealing with significantly fewer bullets. Plus, we already have a solid, lightweight rifle. Weight reductions there are probably going to come from rifle materials, not bullet design. I’m also ok with having a different round for the belt-fed infantry support weapons and the carbines. Linked and loose ammo are basically two different things anyway.
What about the new 6.5 mm projects? That really depends on the goal of those projects. If they’re looking to replace 7.62 mm NATO with a 6.5 mm LSAT round, I’d be okay with that. Or at least, I’d be fine with looking into that and testing the daylights out of that concept. And I would also be fine with a DMR-type ‘heavy rifle’ that fired the same round, in the same vein as the Dragunov rifle.
I would not be happy with any kind of effort to switch the general issue carbine from 5.56 mm anything to 6.5 mm anything. I do not approve of the extra load. I do not approve of adding a whole bunch of extra range that the average grunt can’t use. I do not approve of ignoring a mountain of historical evidence across multiple wars that most infantry combat occurs at relatively short ranges of less than 300 meters. I do not approve of excessively optimizing to fight in Afghanistan. I do not approve of small arms solutions to problems of rules of engagement and airspace deconfliction. I do not approve of any deviation from the classic solution to the sniper problem of mortars and artillery and airstrikes.
Any effort to make the standard infantry rifle a morbidly obese4 affair with a fat, overly energetic cartridge is a return to 1950s US Army Ordnance Department thinking. That nonsense brought us the M-14, which is a piece of junk. Let’s not make the same mistakes of the past. History teaches us what our parents and grandparents did wrong so we can make our own mistakes, not steal theirs.
I’m happy to debate the merits of a different cartridge for the medium/general purpose machine gun role, but that’s a very separate question. And trying for a ‘single cartridge’ means compromising too many ways. Since the SCHV rounds are the least bad present compromise, I’m happy to try out polymer cased telescoped rounds there, where at least the projectile itself can be kept constant.
- Telescoped like the 40mm CTAS rounds, but way smaller of course. ↩
- Even on ‘rimless’ cases like 7.62 NATO. ↩
- This unloaded weapon weight is very nearly replicated in 5.56 mm NATO caliber by the Knights Armament Stoner 96 LMG. ↩
- Projected weight for an empty, opticless 6.5 mm LSAT ‘carbine’ is 8 lbs, which is about 33% heavier than an empty, opticless M4 carbine. It would make a good DMR. ↩
No, the carbine weight will be not the 9.7lbs of the prototype which was sized for 7.62 except for bore and inner chamber, but around 8lbs:
“…The CT Medium Machine gun with 800 rounds of CT ammunition (either 6.5mm or 7.62mm) weighs the same as the current M249 with 800 rounds of brass cased 5.56mm ammunition, and provides far more capability. And when it’s done, the carbine will weigh around 8 pounds, which is more than an M4, but keep in mind the performance exceeds a 7.62mm rifle, which tend to weigh significantly more.”
Kori Phillips, CTSAS program officer, interview on thefirearmsblog.com on 3-25-2017
Fair enough. I was running with the prototype weights from the April 27, 2016 NDIA small arms conference presentation. 8 lbs is a better weight than 9.7 lbs. My objections to general issue still stand, though I’ve edited the weights appropriately. Mea culpa.
P.S. Thanks for the source cite. 🙂
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Sure, glad to help. Ever since I saw the identical figures on the round size for 7.62 vs. 6.5, I thought they must be building both versions with the same dimensions and weight to save time and money. That is, Textron would wait for the Army, Marine Corps, and SOCOM to decide on the caliber before investing in all the work for weight minimizing needed for a finished rifle. That’s a huge amount of time and expense: getting the ideal damping characteristics for both the barrel and stock for best accuracy is never a quick process.
One solution to the ideal caliber problem, as you have well stated it, could be using lighter projectiles in carbines for some battle environments. A single 6.5 caliber for MMG carbine, and DMR could be retained. The case and bullet dimensions (currently a 6.5 Sierra Matchking) would be identical, but recoil would be reduced and muzzle velocity could be the same (used less propellent) or greater for a long battle zero. A 90-100gr bullet with less powder, albeit in an optimized packing density, would have a proportionally lower impulse and less penetration for urban and commando operations. But then the issue is what twist to use: the tighter for the long range rounds or looser for better short-range accuracy? It is possible that the lighter bullets might have superior wounding with incomplete penetration of non-armored targets: all energy dissipated in the body.
The big achievement, if we accept the statements from Textron, is the good accuracy of the newest rounds. Like others I was concerned that the long headspace would condemn LSAT weapons to poorer accuracy vs. AR and M240 platforms, but that appears not to be the case.
The accuracy is really good. Again, if we trust Textron, the maker, and I don’t without independent confirmation. Force of habit.
I figured the same thing on identical 7.62/6.5. And yeah, you could have different rounds, but that’s a massive logistical bother, and it still doesn’t really help the increased weight/bulk burden on the regular soldier. Or the appalling state of marksmanship training these days. I would much rather see something done about that first.
But Big Army seems to not want to really put more money into LSAT, and they’re looking for a new battle rifle. 1952 all over again, sigh.
sorry meant “…for MMG, carbine, and DMR…”
I also meant to say that the carbine could use both the lighter, lower-impulse rounds as well as long-range rounds. The lighter rounds would be for shorter ranges, un-armored enemy, and room-clearing to minimize barrel climb and over-penetration. They could have major LE uses.
One thing I find amusing is people talking about when this hits the civilian market. It will never happen, just drop that notion. I expect all gas-operated weapons will eventually become illegal to carry or sell. But I won’t place a bet on it…
Fun fact on the civie thing. There have been caseless rounds sold on the civilian market before (see Voere’s VEC-91). It performed terribly in the market because most gun owners (especially American gun owners) tend to be super conservative and very reluctant to use new technologies.