"Lieutenant, what do those Pulse Rifles fire?"
"10 millimeter explosive-tip caseless. Standard light armor-piercing round, why?"
Ripley and Lt. Gorman (from Aliens)

10×24mm Caseless rounds loaded into M41A Pulse Rifle MK2 magazines.

The 10×24mm Caseless, designated the M309 in United States Colonial Marine Corps service, is an American-made caseless rifle cartridge notable for being the primary ammunition used by the M41A Pulse Rifle and its variants.[1]


Vasquez fires M41A

Private First Class Jenette Vasquez firing M309 rounds from an M41A Pulse Rifle.

The cartridge consists of a 210 grain (13.6 gram), steel-jacketed and explosive-tipped projectile embedded within a rectangular propellant block of Nitramine 50.[1] Although the propellant mass is small, it is highly efficient, generating muzzle velocities of 840 meters per second. The M309 is optimized for lethality against infantry wearing personal armor, with its factory pre-set impact fuse designed to explode after the round has penetrated armor to inflict maximum damage.[1] Consequently, the round is less effective against unarmored opponents, as it will often over penetrate soft targets without detonating, leaving the victim relatively unscathed and necessitating the use of multiple hits to score a kill.[2]

List of 10×24mm Caseless Firearms[]


M41A MK2 ammo

Checking an M41A MK2 magazine in Aliens: Colonial Marines. Note the erroneous cased ammunition.

  • While the M41 series of Pulse Rifles are said to use caseless ammunition, replacement magazines for the M41A MK2 featured in Aliens: Colonial Marines seem to contain traditional cased ammunition, judging by the metallic color of the rounds, which is easily visible when Cpl. Winter checks his MK2's magazine at the beginning of the game. Moreover, the shape and dimensions of the individual cartridges are vastly different to the 10×24mm Caseless round described in the Colonial Marines Technical Manual, which is actually rectangular in shape.
    • However, any M41A MK2 magazines found lying around the game's levels will have white rectangular shaped rounds in them, closer to what was described in the Colonial Marines Technical Manual.


See Also[]