by MATTHEW MOSS
French gun-maker Louis Debuit’s late-1940s-vintage PM9 was quite unlike almost any other submachine gun. The weapon’s action was a conventional short-recoil mechanism capable of cycling at up to 750 rounds per minute.
However, it was the PM9’s method of slowing the bolt that was so unique. The PM9 made use of a “flywheel” bolt—that is to say, the bolt moved backward and was slowed by a piston-like rotating crank. The connector between the crank and bolt traveled vertically as the bolt cycled.
The bolt and rotating action resembled a piston and crank in motion. Yes, weird.
Debuit originally chambered the PM9 in French 7.65-by-20-millimeter longue, like the earlier MAS-38. However, the manufacturer Merlin Gerin switched this to the nine-millimeter cartridge that had become popular during World War II.
