Earlier this week I published a Reloading Press article on the .277 SIG Fury, a proprietary high-pressure cartridge whose case is constructed in three pieces to handle the colossal 80,000 psi that is needed to meet the latest US Army requirement to fling a 135 grain, 6.8mm projectile out of a 16″ barrel at speeds of 3,000 fps (914 m/s). Depending on what you’re making that bullet out of, you are dealing with a round that is well in excess of a 5:1 aspect ratio, maybe even as high as 5.5:1. Maybe more depending on the tapering at the base.

In any case, that’s the Sig Sauer entry to the Next-Gen Squad Weapon (NGSW) program, and as one would expect dealing with a cartridge that out-pressures even magnum cartridges by 30%, it’s mated to a rifle designed to go with it.

That’s true of all three entries in the NGSW program – they all come with their own ammunition. The .277 SIG Fury is the only one that I’ve seen official stats for.

That being said…we know the requirements. We are also starting to see more and more images, and even videos, of the weapons. Today I want to look at the General Dynamics/True Velocity entry in the competition, the RM277 (277 is the notional caliber of the weapon, which is exactly 7.03mm…but that’s par for the course, as the 5.56mm projectile is also about 5.7mm, so as per always, what a projectile is called and what it actually is bear limited resemblance to each other).

Even so, knowing the requirements, and having some good images of the weapon, we can start to make some conclusions about the system.

The RM277-R and RM277-AR

First, let’s take a look at one of the recent press image of the automatic rifle (a SAW replacement) and what we might call the infantry rifle (an M4/M16 replacement).

One can see, obviously, a few things here, from left to right…

It has an integrated suppressor, identified by others as manufactured by Delta P. This is a “3D printed” suppressor of larger diameter than the usual fare, and reviews suggest that it’s a solid performer, though “not breaking any records” for sound suppression. One interesting thing is that supposedly, the felt noise is lower because the resonance of the suppressed weapon is lower frequency. The Delta P BREVIS II is designed to last “the life of the barrel,” and is capable of being permanently mounted on the end of the barrel, meaning it counts for the overall barrel length. This isn’t important for military users, or law enforcement, but it would be for civilians, for whom barrel length is a legal requirement in the USA.

The -AR version has a longer barrel – obviously – than the rifle version.

Both versions seem to be mounted with a laser sight, have copious rail attachment points.

The charging handle is on top of the weapon, and the handle itself folds flat against the weapon body. I suspect that it’s ambidextrous, either fully, no mods required, or easily switchable.

Lots of rails and attachment points, and a very deliberate 45-degree bevel on the top/side of the weapon…likely for backup iron or red-dot sights, as seen in this promo image (which conveniently shows the -AR version from the other side).

Here’s an important thing: for whatever reason, they have mounted a completely off-the-shelf AR-15/M16 grip on it. Ergonomics, familiar feel? Sure. But one thing about that? I own one. That handle is 110mm from the top left of the attachment to the flat on the bottom of the grip.

That lets me calculate barrel length, or at least approximate it. From the beginning of the suppressor to the front of the magazine well, on the infantry rifle that length is 4.558x the length of the grip. That’s about 500mm (19.7″…basically a standard 20″ barrel). The automatic rifle is 5.288 times the length of the grip. That’s 582mm, or 22.9″. Since customarily the US includes the length of the chamber in the length of the barrel, we can conclude that the weapons were designed with approximately 20 and 23″ barrels. That also allows an estimate of the length of the weapons: 916mm (36″) for the automatic rifle including the suppressor, and a scant 851mm (33.5″) for the infantry rifle version.

We have a box magazine in both cases; that’s almost a throwback to the Browning Automatic Rifle. I’m not entirely sure why that’s going on, but I have to wonder if that will change over time. Given the one-piece look of the rifle body, I don’t see an easy way to do a belt…assuming that’s a requirement. For a rifle touting sustained automatic fire, though, one would think more than the 20-30 rounds would be desired. Given the touted 30-40% weight reduction of the TVCM ammunition due to the case, a 100-round C-MAG dual-drum equivalent should come in at something like 6-7 lbs (based on the 10-11lb weight of a loaded CMAG in 7.62x51mm). I’d think that “fire and forget” in both weight and links is superior to what will certainly be a desire to bring the empty magazine home with you with the larger drum. That’s speculation. A 200 round box of 7.62 with links seems to weigh 15-18 lbs, though.

And now my favorite, totally biased part: it’s a bullpup. Mmmm. Yummy. That’s been obvious the whole time, but I had to wait until the end because I was going left to right. I suppose I could have mentioned it when I got to the grip area, since on a conventional rifle the magazine well would be there.

One side of the weapon has what looks like a plate, the other a cartridge-shaped hole. So I’m presuming the ejector for spent cartridges is reversible.

Finally, at least to me, the stock of the weapon is adjustable; looks like maybe 75-90mm of adjustment, and I see 5 detents in the side-on image, spaced 15mm/0.6″ apart.

One thing not obvious from the image: it is said to fire in closed-bolt mode for semi-auto fire, and open-bolt in full-auto mode.

Finally: nothing is set in stone until it is. The Firearm Blog has some great images of a “next” version, which makes the adjustable stock even more obvious, and some other changes, including a bolt release. Read their article.

The Ammunition: 6.8 TVCM (6.8x49mm?)

There are two ways to look at how they approached this. Firstly, we can get some dimensions from the case. If we assume the bullet is 6.8 to 7mm in width, we see the case is about 1.655× wider than this (11.25 to 11.59mm). The 6.5 Creedmoor is a bit wider, averaging 11.8mm between base and shoulder; the .308 Winchester varies from 11.96mm at the base to 11.53 at the shoulder. So this is a bit more svelte than the 6.5 Creedmoor. The case is therefore 6.941× the width of the bullet, or about 48-49mm long. So the combustion chamber, so to speak, formed by the cartridge case is not appreciably larger than any other cartridges in its class.

Based on the .277 SIG Fury, there are two ways to approach this. One is to say “the requirements are what the requirements are,” and that means that in this case, you still need to fling a 135gr bullet down a 16″ barrel at 3000fps. But the chamber is smaller, so you’re going to need even more pressure, OR have the pressure be maintained for longer. I did notice on the .277 SIG Fury that there was probably room to do that, in that the design team seems to have chosen a very fast-burning powder.

Also: this is using my spreadsheet, which is definitely not as good as a real combustion calculator. But I’m rolling with it because it’s what I have.

Even so: With about an 11.4mm chamber diameter and a 49mm chamber length, a “burn length” of up to 31mm isn’t crazed. It’s not even excessive. That allows the pressure to drop to “only” 74,000 psi to get that kind of performance that meets the requirement.

Of course, the RM277-R barrel is 500mm long, not 406. So either we develop a screamin’ 970m/s out of the same projectile, or they can take advantage of that extra barrel length to lower the pressure down to only 65,860psi. Well, well, well. That’s not small, but it’s rather a lot closer to the 64,000psi of the Winchester (Short, Super-Short, and regular) Magnum rounds. If we allowed for an even slower-burning powder which kept pressure higher at 65,000 psi for longer and a 16″ barrel requirement, we’d need a 54.3mm “burn length.”

I have this mental rule where if 10× the “burn length” is going to be longer than the barrel, you’ll have issues with flash and unburned powder.

Hrm. And yet what we have here is a suppressor that is designed for the life of the barrel, can be permanently mounted, and adds another 125mm to the barrel length. And it’s not “real” barrel length…it’s a flash-hidin’, noise-reducin’ set of baffles.

You know what? I may well be wrong, but I’m going to speculate that’s what TVCM is going to do: Sustain a lower pressure for longer. That being said, another news release did say that the TVCM case is tested to 80,000 psi. So all bets are off in terms of what’s actually going on. I note the high pressure, short burn produces a higher velocity in the longer, 580mm barrel. So the two aren’t equivalent, and the higher pressure, shorter burn load will deliver a white-hot 1047m/s.

Watch the Movie

One of the bits of marketing speak is that the RM277 is said to be an “impulse averaging” system. OK.

But one thing I noticed, and it’s most visible in the following marketing video at 0:27 to 0:33 or so – the suppressor is actually moving backwards. That means the barrel is moving backwards too.

Check it out:

You know what other weapon had the barrel, ammo, and action recoil together such that three rounds could leave the barrel before the recoil was felt by the shooter? The Heckler and Koch G11.

(Oh, and note that the 45-degree bevel is shown most excellently in the freeze-frame that starts this movie, hosted on The Firearm Blog, and yes, indeed, there are backup iron sights for close-in work.)

Parting Shot

The weapon requirements are what they are. So if every cartridge must meet the 3000fps requirement out of a 16″ barrel, well…there are only so many ways to get there.

However, that doesn’t mean later ammunition can’t be tuned to be more forgiving on the weapon system. In fact, were I the US Army, one would have to wonder if “only” firing a 65,000psi cartridge out of said bullpup rifle and still meeting the 3,000fps criteria in a weapon that’s only 33″ long WITH a suppressor isn’t a better all-over solution to the question. Recall that 33″ is the length of the M4 carbine with the stock extended for firing, but with only a 14.5″ barrel and no suppressor. This is where the bullpup configuration shines, as it gives a full-length barrel and a noise level congruent with “loud but not hearing-loss loud” in a package the same size as the M4 with none of those things. I can’t help but think this is quite deliberate.

I haven’t spoken about the automatic rifle yet. I can’t help but think that the lack of an obvious sustained fire ammunition capability is a detriment. That being said, there are lots of ways to skin that cat, and there are extant pictures of linked True Velocity ammunition. There’s no obvious way to do it, but as quoted in the linked Firearm Blog article (bold added):

The RM277 AR has a heavier profile barrel but both weapons feed from 20-round box magazines. This is something that has been raised as a potential issue by some as the automatic rifle is intended to be a SAW replacement. Beretta said that as yet the Army had raised no concerns about the magazine’s capacity and pointed to the USMC’s choice of the box-magazine fed HK416 as the M27 IAR – with accurate suppression being favoured over volume of fire. Despite this Beretta did say that if necessary they were confident larger capacity magazines could be developed.

The “impulse averaging” technology, almost certainly related to the method used on the H&K G11 if the video is any indication, is quite cool. In GURPSy terms, it’s going to be what’s needed to make a weapon that’s nominally Rcl 3 brought down to an M16-like Rcl 2.

We really won’t know it all until we know it all. And of course, the history of “M16 replacement” programs is dismal and horrible.

But I leave with two thoughts:

First: The Firearm Blog really does a nice job of grabbing a lot of this stuff. Here’s their NGSW tag, but they compile lots of other great info.

Second: I’m biased. I want the bullpup to win, if the program actually comes to fruition. I love how my M17S handled…and that’s not a great example of a well-tuned bullpup. I want to try a more modern design “for reals,” like the Tavor X95 or the Desert Tech MDRx.

Stats

Talk about rampant speculation? Let’s do this. We’ll assume that the rifle delivers its projectile – more or less the same as the .277 SIG Fury – at 914.4m/s from a 406mm barrel, which means it’s faster out of the 500mm barrel.

• TL: 8+
• Weapon: RM2777-R, 6.8x49mm TVCM
• Damage: 8d+1 pi
• Acc: 5
• Range: 700/5,200
• Wt: 9.3/1.0
• RoF: 12
• Shots: 20+1
• Bulk: -4
• Rcl: 2
• Cost: Dream on, for now. But probably $2,500/$35

Notes: This is a magnum rifle in how it’s chambered: high pressure plus tons of energy. So it’s probably kickin’ it similarly to the Magnum Rifle category in High-Tech, that is: audible on on unmodified hearing roll at between 1,000 and 1,300 yards. With the suppressor, it should knock it down to about 135dB, so by 25-30dB; let’s give it a full 30 dB, though numbers of 32 and even 37 dB of reduction are not unusual these days. That should drop the “range” for an unmodified hearing roll by a factor of 8-10x, meaning the “true” range should be as low as 100yds and as high as 162 yds. That makes it basically a -3 to Hearing suppressor for GURPS terms, and call it a nominal range for an unmodified Hearing roll of 150yds using the method in High-Tech. That might not be the best one out there…but it’s the ONLY one that I know of, and it’ll make it consistent with the values in High-Tech and Tactical Shooting, which has value for a game.