This weapon is best known by the name JM Reibel.
JM stands for Jumelage de mitrailleuses which means twin machine gun mounting.
Reibel is the name of the director of the state owned arms factory (MAC) were
it was developed and produced. MAC stands for Manufacture d’armes de Chatellerault.
The basis for this weapon was the single MAC Mle (= model) 31, often shortened as MAC 31.
In 1930, the FM 1924/1929 light machine gun was used as a basis for the MAC 1931. The main difference was that the MAC 1931 made use of a drum-fed magazine (150 rounds). This resulted in a higher rate of fire. Eventually, it was rejected by the Infantry.
|Magazine capacity||150 rounds|
|Max. range||4900 m|
|Rate of fire||See text|
|Muzzle velocity||694 m/sec|
However, it was well suited for use in the Maginot line when used on a twin-mount. This configuration made it possible to make use of one weapon, while the other could cool down. In particular situations, both guns could be used at the same time. This machine gun configuration was used in many cupolas, turrets and concrete/casemate positions.
The practical range was 1,2 km’s (2,4 km’s when the ammunition model D (Model 1929 D, see page 3) was used). Maximum range was up to 4900 meters. It was gas operated.
The interval casemates had two of these JM’s equipped (e.g. in case of a single casemate: a double casemate had 4 of them). In a firing chamber, one of the 2 JM’s had to share an embrasure with an AT gun. During combat, changhing weapons was a hazardous situation: for a short period of time the embrasure would be opened like a window!
When there were just two JM’s in a firing room (so no AT gun), 8 men operated the weapons. 2 Gunners, two loaders, 2 assistant loaders, a mechanic and a commander. As already mentioned, normally one machinegun per twin-mount was used. When it became overheated, the second machine gun was put into action.