The Reibel machine gun is a gas operated weapon chambered in the 7.5 mm MAS cartridge and was loaded with vertical, side-mounted, 150-round pan magazines.

Some other guns in French service during the late 1940s were converted to ground role, with adoption of the side-mounted 35-round box magazines and adapters for US M2 tripods.

It is derived from the French FM 24/29 Fusil-Mitrailleur (light machine gun) also designed by Lt Colonel Reibel, and based on the Browning Automatic Rifle.

The FM 24/29 was developed into a heavier machine gun capable of relatively sustained fire, by giving it an extremely thick and massive barrel, to act as a heat sink.

[citation needed] The standard for a mle 1931 in fixed emplacements was a JM Reibel twin-mount, complete with telescopic sight, azimuth and level indicators, elevation screw and spent case ejection chutes.

This ensured that there were no gaps where enemy bullets could enter into the bunker (except the very small opening that the telescopic sight peeped through), yet allowed the guns to be aimed and trained on anyone outside the walls.