RCBS Chamber Case Length Gauge - 300 Winchester Magnum - The RCBS Chamber / Cartridge Gauge is a one-piece, non-adjustable gauge designed to check all critical dimensions of ammunition to insure proper fit. Quickly check case length, diameter, and the overall cartridge length of your handloaded ammo. 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 Quickly check case length, diameter, and the overall cartridge length