This Exotic Bullpup Rifle Is Competing To Replace The Army’s M4 Carbines And M249 SAWs

Of the companies competing to build the U.S. Army’s next standard infantry rifle and squad automatic rifle, both of which will use new 6.8mm ammunition, only one offering has a so-called bullpup configuration where the main action is positioned behind the pistol grip. There are benefits to this arrangement, namely the ability to maintain the accuracy that a longer barrel offers in a more compact package, but the U.S. military as a whole has rejected them in the past in favor of more traditional designs.

General Dynamics Ordnance and Tactical Systems (GD-OTS) first unveiled its RM277 small arms line at the Association of the U.S. Army’s main annual convention in Washington, D.C., which opened on Oct. 14, 2019, and wrapped up today. The Firearms Blog was first to report the guns’ designation, as well as other details about the particular features of the infantry rifle and automatic rifle variants that have emerged so far. However, GD-OTS has been relatively tight-lipped about the weapons, which are competing in the Army’s Next Generation Squad Weapons (NGSW) program, which aims to replace the service’s 5.56mm M4 carbines and M249 Squad Automatic Weapons (SAW). The company told The Firearms Blog that its policy is not to issue formal press releases regarding systems taking part in “an active, open competition.”

As noted, the basic design of both RM277 variants is a bullpup with the action, along with the magazine, situated all the way to the rear. They both also feature a large top-mounted rail for optics, night and thermal vision systems, and other accessories. There are back up sights offset to the side and there appear to be attachment points for additional rails on the sides and underneath the forend handguard.

The automatic rifle variant, which has a folding bipod, has a slightly longer barrel than the rifle version, but we don’t yet know the exact dimensions of either model. The barrel on the automatic rifle version, intended for more sustained fire, is clearly fluted to reduce weight and help it cool faster. It is possible the one in the basic rifle design is, as well, and it is just not visible.

GD-OTS’ RM277 automatic rifle variant, at top, and infantry rifle version, at bottom., GD-OTS via The Firearms Blog

Both guns fire a 6.8mm round, with a polymer case rather than a brass one to keep weight down, that ammunition maker True Velocity developed to go along with the guns. All of the NGSW entrants will have to be chambered in this caliber. 6.8mm is roughly .277 caliber, which is the origin of the “277” in the RM277 designation.

The U.S. military has been exploring polymer cases for years as a way to reduce how much weight individuals troops have to carry and it has begun to buy such ammunition, and rounds that use hybrid polymer-metal cases, already. These developments are extremely innovative and notable in their own right.

True Velocity’s 6.8mm cartridge design., True Velocity

The Army has also required that the NGSW submissions come along with a suppressor. GD-OTS has chosen an unusual-looking design from Delta P Design that is shorter and wider than many traditional suppressors to go along with the RM277.

Most interestingly, both guns use a novel “gas and recoil-operated, impulse averaged, air-cooled” operating mechanism, according to The Firearms Blog. It’s not entirely clear how the guns function, but the description suggests that they use a combination of physical energy from firing a round, as well as propellant gas siphoned off as the bullet travels down the barrel, to cycle the action. By comparison, the U.S. Army’s standard M4 carbine uses propellant gas alone. 

A promotional video below shows that the barrel on the RM277 versions moves back and forth during firing, which is indicative of so-called “long recoil” designs. Though the basic concept of a long-recoil action has been around for decades, they have become increasingly rare and pairing it together with a gas system would be very unusual.

In principle, using a combination of long-recoil and gas-operated action could help mitigate felt recoil, which would improve accuracy, even during fully automatic fire. This could also help keep weight down, by minimizing the force firing each round exerts on the weapon and, in turn, reducing the need for more robust recoil system components. Combining all of this will a bullpup configuration could also ensure maximum barrel length without needing to dramatically increase the overall length of the weapon to accommodate this operating mechanism, as well.

It will be interesting to see how the RM277s fare in the NGSW competition. Bullpups offer advantages over traditional designs, including being able to be more compact without necessarily sacrificing barrel length and the associated accuracy that a longer barrel provides. At the same time, the mechanical linkages necessary to connect the trigger in front to the main action behind do not lend themselves to precision fire.

In addition, though armorers can configure many designs, including the RM277, to eject cartridge cases from the left or right, to suit left- or right-handed operators, this cannot be done in the field, which can make offhand shooting in complex, constrained environments more difficult than it might already be. Critics have often cited potential difficulties in reloading, especially while lying prone or in otherwise awkward positions. 

GD-OTS via The Firearms Blog

Proponents have countered that sufficient training could mitigate or eliminate many of these concerns, but there continues to be an intense debate over the pros and cons of bullpups versus more traditional configurations. It is worth noting that many national militaries around the world have gone back and forth themselves, with the Chinese just recently introducing a new standard infantry rifle in a conventional configuration after decades of using bullpups.

The RM277 designs also have potential maintenance and logistical benefits in that the infantry and automatic rifle variants share the same action, upper and lower receivers, and the vast majority of their other key components. This would reduce the number of unique spare parts and tools necessary to service the guns.

The other two NGSW contestants, Textron’s AAI division and Sig Sauer, have each submitted two distinct weapon designs to meet these separate requirements. Their automatic rifle variants are both belt-fed, rather than magazine-fed, as well. You can read more about Textron’s entries in this past War Zone piece. Sig Sauer’s offerings are derived from the company’s increasingly popular MCX line, which is itself a piston derivative of the AR-15/M16 family that the U.S. military already uses.

Sig Sauer’s automatic rifle entry, at left, and its infantry rifle design, at right., Sig Sauer

How much any of these designs might further evolve as testing gets underway remains to be seen, too. The Army hopes to pick final infantry and automatic weapon designs in 2022 ahead of actually beginning to field the new guns the following year.

Regardless, with the RM277 in the competition, there is now the possibility that U.S. Army troops may be starting to use these exotic and unique bullpup rifles and automatic rifles four years now.

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Joseph Trevithick Avatar

Joseph Trevithick

Deputy Editor

Joseph has been a member of The War Zone team since early 2017. Prior to that, he was an Associate Editor at War Is Boring, and his byline has appeared in other publications, including Small Arms Review, Small Arms Defense Journal, Reuters, We Are the Mighty, and Task & Purpose.