With the end of World War One, it was finally possible for the French military to replace the 8mm Lebel cartridge with a modern rimless cartridge, and they wasted no time in doing so. By 1924 a new round had been adopted, and along with it a new modern light machine gun. Next, the arsenals would start working on converting 8mm rifle to the new cartridge. The first candidate was the Lebel, and in 1927 a conversion was approved and a batch of a few hundred made - but this was a more expensive and time consuming process than anyone wanted. After some brief trials, it was decided to work on adapting the Berthier instead, and in 1934 a conversion designed from St Etienne was approved as the 1907/15-M34.

This new design used a new 22.5" barrel (570mm), a Mauser style internal 5-round double stack magazine, and new sights. The receivers and trigger parts were retained from the rifles being converted, along with the nosecaps and barrel bands, but not much else. Still, these conversions were put into production alongside the manufacture of new MAS-36 bolt action rifles. By the time of the German invasion about 63,000 M34 Berthiers had been converted, and were issued to frontline troops. They would fight in the Battle of France, and would also be used by German occupation forces as the Gewehr 241(f).