.300 Ruger Compact Magnum

The .300 Ruger Compact Magnum or .300 RCM is a rimless, short-length rifle cartridge designed for the hunting of medium-to-large-sized North American game. It is designed to closely duplicate the performance of the historic .300 Winchester Magnum cartridge, yet to be chambered in a short length action rifle.

Source: Wikipedia — .300 Ruger Compact Magnum (CC BY-SA 4.0)