Simply drop a loaded round into the precision made gauge, and if your cartridge fits the gauge, it'll fit your pistol. Gauge checks both chambering as well as cartridge length. Quickly confirms ammunition will fit your pistol's chamber Easy-to-read engravings display caliber size The RCBS Chamber / Cartridge Gauge is a one-piece, non-adjustable gauge designed to check all critical dimensions of pistol ammunition to insure proper fit.