France fought the Great War with an array of weapons which were all sub-par in one way or another – the Lebel rifle was obsolescent by 1914, the Berthier was a cavalry carbine forced into rifle service, the Chauchat was an emergency wartime design optimized for production volume instead of quality, and the handguns were a mixture of old revolvers and desperate imports from Spain. Once the war finally ended, the French military would move to replace the whole lot with new and modern arms.
This would begin by finally replacing the 8mm Lebel cartridge with a non-tapered, rimless cartridge – something that would be well suited to use in magazines and repeating arms. Simultaneously, a new light machine gun would be found, as this was deemed to most important improvement to be made. The cartridge was adopted in 1924 as the 7.5x58mm, but it would soon be realized that there was a critical problem with that round. The French military had a large supply of German arms taken as war reparations, and the new 7.5mm cartridge looked very similar to the 8x57mm Mauser cartridge. Worse, the Mauser round would chamber and fire in the new French chambers, causing serious damage to guns when the 8mm bullet was squeezed down to 7.5mm. To fix this issue, the French cut their cartridge down by 4mm, resulting in the 1929 adoption f the 7.5x54mm round – the chamber of which would no longer fit a German round.
As for the machine gun, the first choice was to simply adopt the Browning BAR – but France insisted on obtaining the technical data package and producing the guns in France, and they could not come to an agreement with Colt over the price of such a license. So, the French held trials of other guns, looking at virtually everything then available. In the aftermath of the trials, it was decided that the Chatellerault arsenal could design its own weapon using the best features of the other existing guns. The arsenal rather quickly produced prototypes, and they were adopted in 1924 (and then updated to use the shorter version of the 7.5mm cartridge in 1929).
The Chatellerault M24/29 is a quite good weapon, especially considering how early it was designed. It uses a tilting bolt and a top-mounted 25 round magazine. It has two triggers, the front one firing in semiautomatic and the rear one in fully automatic. The wooden front handguard allows for fire from the hip or shoulder if desired, and a set of thorough dust covers keep the gun free from ingress of mud or dirt. About 188,000 would be manufactured, and it would stay in service for many decades.