In the aftermath of World War One, the French military instituted a plan to introduce a completely new roster of small arms. This would begin with the development of a modern rimless rifle cartridge, which was adopted in 1924. With the new cartridge in hand, programs were begun to develop a light machine gun, bolt action rifle, and semiautomatic rifle using it. To supplement these new arms - especially during their development and production - plans were also made to convert existing 8mm rifles to the new cartridge.
The two rifles in large supply, of course, were the Lebel and the Berthier. The St Etienne arsenal was tasked with developing a Berthier conversion (this would become the M34 Berthier), and the Tulle arsenal was assigned to do the same with the Lebel. The first prototype was ready for testing in 1927. That first example was not satisfactory, and iterative development would continue into the early 1930s. Ultimately, the Lebel conversion was simply not as well liked by troops or as effective as the M34 Berthier, and so the Berthier was chosen for mass production. A total of about 1500 Lebel M27 conversions would be made by 1940, in a wide variety of configurations including different barrel lengths, rifling patterns, and optics mounting setups. While this did not result in a successful production rifle, it would inform the development of the MAS-36, and not go to waste. In addition, a number of M27 rifles would be converted into pressure testing guns to assist in ammunition development.