A bullet in a plastic casing: how a firearm fights its own weight
A prototype Textron Systems light machine gun being tested for the U.S. Army's Next Generation Squad Weapon (NGSW) program. This machine gun was developed as a replacement for the M249 SAW machine gun, using telescoped ammunition.
A rifle bullet weighs a few grams: it's the bullet that flies to the target. Everything else falls short: the gunpowder burns, and the brass casing flies out at the shooter's feet. But the entire cartridge has to be carried, and here comes the unavoidable arithmetic. A thousand shots equal kilograms of metal, existing for the brief milliseconds of a shot. Is it possible to reduce the weight of a cartridge without sacrificing its lethality? Small arms engineers are exploring this question. weapons have been fighting throughout the 21st century.
Excess metal: why the cartridge case became ballast
Ammunition weight is a perennial pain point for infantry. The cartridge case in a standard cartridge accounts for a significant portion of its weight and yet bears no combat load: its job is to obturation (seal the propellant gases in the barrel) and feed the cartridge, nothing more. For decades, this was tolerated because brass is reliable, technologically advanced, and forgiving of overheating. But the price of reliability is excess metal in every round carried.
Small arms won the first major "weight war" in the mid-20th century, but without changing the case: weight was reduced by reducing the cartridge size. Full-size rifle cartridges—7,62×54R, .30-06, and 7,92×57mm Mauser—offered range and energy, but were heavy, produced stiff recoil, and, due to their weight, limited the ammunition carried. The transition to an intermediate cartridge after World War II—7,62×39mm, then 5,56×45mm NATO and 5,45×39mm—cut both weight and recoil simultaneously. Light machine guns had existed before, chambered for rifle cartridges: the Soviet DP (DP-27), the American BAR, and the German MG 34 and MG 42. But it was the intermediate ammunition that pioneered the concept of the light squad machine gun—from the RPD to the later SAW (Squad Automatic Weapon) class, which includes the American M249, a machine gun carried by a soldier as part of his personal equipment.
By the beginning of the 21st century, the problem had returned from a different angle. A soldier was no longer just a rifle and some pouches: he now carried a radio, night vision goggles, a navigator, and a heavy-plated body armor. Each new piece of equipment consumed a few grams, and ammunition became the reserve that needed to be trimmed. The logic was simple: remove weight from the ammunition loadout, either give it to electronics or leave it to the soldier as a mobility reserve.
Caseless or telescoped cartridges. They were developed as part of the Lightweight Small Arms Technologies (LSAT) program to reduce the weight of ammunition.
Telescopic Chuck: LSAT's Radical Solution
The most daring response to this challenge was provided by the American Lightweight Small Arms Technologies (LSAT) program, launched in the 2000s. Rather than lighten the machine gun's secondary components, the designers focused on the cartridge itself. They approached it from two angles: the case material and its shape.
The first solution was a polymer case instead of brass. Plastic is several times lighter than metal, and this alone promised significant savings. The second was a telescopic cartridge, in which the bullet doesn't protrude, but is completely recessed into the case. Externally, it's a short cylinder, resembling an industrial wad. It's completely unlike a conventional cartridge with a protruding bullet: it's more compact, easier to handle, and even lighter.
The experimental LSAT LMG was built on this basis. Its gas-operated system and open-bolt firing are similar to classic belt-fed models, but its feeding system is unique: a rotating chamber chamber chambers telescoped cartridges. Its rate of fire is approximately 650 rounds per minute. However, the interesting thing isn't the design, but the savings figures. According to the developer, the "LSAT machine gun plus 1000 telescoped cartridges" kit is 20,4 pounds (over nine kilograms) lighter than a similar kit based on the M249 SAW with standard brass cartridges.
Nine kilograms is the weight a soldier either carries throughout a battle or doesn't. These nine kilograms are the main purpose of the program. But there was a second advantage: thermal. According to testing results, the chamber design allowed for over 250 rounds of continuous firing without the risk of "cook-off," or spontaneous combustion of the cartridge due to an overheated barrel. In the M249, under certain conditions, such overheating occurred after about 220 rounds of continuous firing. It's worth remembering, however, that all these figures are based on the firing range, and in real combat, fire discipline is more important than the ultimate performance of the weapon.
Why the breakthrough remained a prototype
The results are in: lighter, cooler, and the soldiers liked it during testing. And yet, the LSAT LMG never went into production, remaining a prototype. In the arms industry, such stories outnumber high-profile successes; they're simply less frequently reported.
There are several reasons, and none can be reduced to a simple "it didn't work out." Despite all its advantages, polymer cartridges pose their own challenges: performance under high pressure, service life, operation in cold and hot conditions, and extraction reliability. Brass has solved all these problems for a hundred years, and every deviation from it must be proven anew, shot after shot. And most importantly, inertia: the entire world, from factories to warehouses, is designed for metal cartridges. Switching to a fundamentally new cartridge means redesigning not just one machine gun, but the entire chain, from ammunition production to field supply.
Weight is reduced, yes. But not indefinitely, and certainly not for nothing. Every kilogram saved is paid for with risk, cost, and disruption to traditional logistics. LSAT proved that radical weight reduction was technically feasible, and immediately explained why the army was hesitant to adopt it. It confirmed the idea, but never became a weapon. And that was the end of it.
Successors: hybrid sleeve and silencer as part of the system
The LSAT's ideas haven't disappeared; they've been channeled into more cautious designs, blending innovation with proven metal. The most notable successor is the 6,8×51mm cartridge from SIG Sauer, developed for the American Next Generation Squad Weapon program. Its case is hybrid: a brass body and a steel base. This compromise, a redistribution of material, allows for higher pressures with less weight than a solid brass cartridge. This cartridge is also chambered for the M250 light machine gun, which entered service with the US Army in 2023.
True Velocity is following a similar path, but further toward polymer, with its composite case for the .338 Norma Magnum cartridge in the RM338 machine gun. According to the company, the composite case reduces the weight of the ammunition, exactly the same logic that guided the LSAT. The difference is that now, lightening the cartridge is no longer an end in itself but part of a broader system: along with the new caliber, optics, and fire control.
A second line of development is underway: reducing visibility. Silencers, commonly known as suppressors, have ceased to be a sniper's tool and have become standard equipment on machine guns. The KGM LMG-SD is a prime example—a suppressor specifically designed for sustained fire and, according to the manufacturer, for common machine guns: the M240, M249, M60, and the Russian PKM. Its purpose is not only to muffle the shot but also to eliminate muzzle flash, reduce the barrel's thermal signature, and divert propellant gases away from the shooter.
New systems come with a suppressor built right in. SIG ships its 6,8mm light machine gun with a proprietary suppressor designed for the high pressures of the new cartridge: according to the program's design, it's part of the package, not an add-on. The goal is the same as weight reduction: to make the shooter's job easier. Only now, it's not about the weight they carry, but about visibility. Thermal imaging and acoustic reconnaissance capture every flash, every hot barrel, and the suppressor takes away these clues.
Brass isn't going anywhere just yet: the global weapons inventory and ammunition reserves are too vast to replace the case with a single solution. But the direction has been set, and the first compromise has already reached production: the 6,8mm hybrid cartridge is more conservative with weight than the LSAT, but it's in service. The telescopic cartridge in a plastic case is still biding its time, and judging by the increasing burden on the infantryman, it will.
Information