10x24mm caseless
Vital statistics
Type Ammunition
Effects Unknown
Source Armat Battlefield Systems
Cost to buy
Cost to sell Unknown
Quote1 Lieutenant, what do the pulse rifles fire?
10 millimeter explosive-tip caseless. Standard light armor-piercing round, why?
- Ellen Ripley and Lieutenant Scott Gorman

The 10×24mm caseless, designated the M309 in the service of the UNSC Marine Corps, is a caseless rifle cartridge that is used as the primary ammunition for the M41A pulse rifle and its variants.



Private First Class Jenette Vasquez firing 10x24 rounds from her 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. 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. 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.

10x24mm firearms