A 9x18mm round in real life.
The 9x18mm cartridge was originally designed for the Makarov PM however after subsequent years it has been adopted by other eastern bloc sidearms such as the Fort-12. The 9x18mm cartridge is very common and cheap and readily available from most traders. The 9x18mm has no direct NATO equivalent but somewhat the Soviet version of the 9x19mm Parabellum cartridge.