The US Army is developing the LSAT (Light Small Arms Technology) program with the task of creating a new “weapon + cartridge” complex that can significantly reduce the mass of equipment carried by a soldier and weapons, while maintaining combat capabilities.

The main contractor for this program is the American company ATK. Initially, within the framework of the LSAT program, it is planned to develop a light hand machine gun and cartridges for it, followed by the creation of a new machine gun and other types of small arms for the same cartridge.

Since the main characteristics of any small arms complex are always primarily determined by ammunition, work on the LSAT program was initiated with the development of light cartridges of 5.56 mm caliber. At the same time, two ways of working were chosen – the creation of caseless cartridges as a more radical way, and the creation of cartridges with a plastic sleeve as a replacement.

The purpose of the LSAT program was to reduce the weight of the “machine gun + 600 ammunition” complex by 50% compared to existing systems (M249 SAW machine gun).

Currently, machine guns with cartridges with plastic sleeves and cartridges for it have been successfully created and tested, the first tests of a machine gun with a sleeveless cartridge were also carried out, and a prototype of a machine gun (carbine) was made. The LSAT system was created.

The basis of the LSAT small arms complex are new 5.56 mm cartridges, which use the same bullets and provide ballistics similar to standard 5.56 mm NATO cartridges.

LSAT cartridges are created in two versions with a similar layout – sleeveless and with a cylindrical plastic sleeve. In both cases the bullet is completely immersed in the propellant and the cartridge is shaped like a simple cylinder. Uncased cartridges have slightly smaller dimensions and weight, but are more expensive to manufacture. One 5.56 mm caseless LSAT cartridge weighs 6.3 grams, while the plastic cased cartridge weighs 8.3 grams. For comparison, the 5.56×45 M855 cartridge weighs 12.2 grams.

LSAT machine gun cartridges are equipped with a loose tape assembled from light plastic links. As a result, 600 rounds for the LSAT machine gun in tapes weigh from 4.6 kg (without casing) to 5.8 kg (with plastic casing), while 600 rounds of 5.56 mm M855 in tapes weigh 9.4 kg.

LSAT machine guns usually have the same design for both caseless cartridges and plastic sleeve cartridges. The main differences are in the design of the mobile room obturation unit, which is more complex for the armless version. The machine gun uses automatic gas relief with a gas piston located under the barrel.

The machine gun has a movable chamber that tilts sideways around the horizontal axis so that the machine gun mechanism can push the next cartridge out of the belt link and forward, directly into the chamber. When sending, the cartridge pushes the spent cartridge case (if any) out of the chamber so that it falls out of the weapon through a special window. After sending, the chamber moves back, becomes coaxial with the barrel, and a shot is fired. The shot is made with single shots and bursts. The cartridge tape is placed in elastic boxes with a capacity of 150 cartridges, which are attached to the machine gun from the bottom.

The LSAT carbine also has a separate movable chamber, but in it the reload chamber does not tilt to the side, but falls down (similar to the Steyr ACR). Cartridges are fed into it in a backward motion from a separate 4-row box store, used cartridges (if any) are also withdrawn from the chamber with a new cartridge and fall through the window in the receiver.

Tactical and technical features:

• Caliber, mm: 5.56, with or without plastic sleeve
• Weight, g: 4200 – 4500
• Tape capacity, cartridges: 150
• Rate of fire, in/min: 600