As a result of the general obsolescence of the 8mm rimmed cartridge and the need for a better light machine gun, soon after WW1 the French army started its infantry rearmament program with the development of a new cartridge, suitable for use in automatic weapons. The basic pattern of new ammunition was adopted in 1924; it was a 7.5x58 M1924C rimless cartridge. In 1924 after extensive trials the French army adopted a light machine gun, developed since 1921 by another state-owned armory, Manufacture d’Armes de Chatellerault, or MAC for short. Production of the new gun, designated Fusil Mitrailleur Mle 1924 (or FM M1924 in short) commenced in 1925. During the next few years, the new cartridge caused certain problems, mostly because it was dimensionally very close to the German 7.92x57 ammunition (used by certain French units in ex-German MG.08/15 machine guns), so it was possible to load and fire German 7.92mm ammunition from 7.5mm French guns – although rarely more than once per gun. To avoid further problems, in 1929 the French army adopted a modified version of the 7.5mm round, with the case shortened to 55mm, so accidental loading of the longer German ammunition became impossible. MAC M1924/29 light machine gun served as a standard light machine gun for French army through the WW2 and Indo-china conflict of 1950s.
The MAC Mle.1924/29 (Fusil Mitrailleur Modèle 1924 M29) light machine gun is a gas operated, air-cooled, selectively fired weapon. It fires from an open bolt. The barrel can be detached from the weapon only in armory. The basic action consists of a long-stroke gas piston, located below the barrel, enclosed within a gas tube. The gas system is non-adjustable. Locking is achieved by tilting the rear of the bolt up and into a locking recess cut in the roof of the receiver. The tilting motion of the bolt is controlled by dual swinging links, which connect the rear of the bolt with the operating rod that forms the rear extension of the gas piston. The firing pin is permanently fixed to the vertical projection made on the top of the operating rod; therefore, it can strike the primer only when bolt is fully in battery and locked. The trigger mechanism has two triggers, which produce different modes of fire – pull on the front trigger results in semi-automatic fire (single shots), while pull on the rear trigger results in automatic fire. A manual safety lever is located above the triggers and locks both triggers when engaged. This machine gun is fitted with an inertia-type rate reducing mechanism. The feed system uses dual-row box magazines, inserted from the top. Fired cartridge cases are ejected to the right through an ejection window in the receiver. The magazine aperture has a steel dust cover, which opens up forwards when gun is loaded. The same dust cover carries an additional hinged cover on its right side, which closes the ejection aperture. Standard sights include a front sight, installed on the barrel, and a tangent-type rear sight with a diopter aperture, located on the top of receiver behind the magazine housing. The sight line is offset to the left since the gun uses top-fed magazines. Standard furniture includes a short wooden forend below the front of receiver, a wooden butt with a hinged shoulder rest and a pistol grip. A folding bipod is attached to the barrel just behind the front sight base.