Abstract: Provided is a centerfire rifle cartridge. A case has a head end, an open mouth end for receiving a projectile, and a central axis. The head end has a base portion substantially conforming to that of a .50 BMG cartridge. The case has a case wall with a taper of up to 1.0° relative to the central axis. A frusto-conical shoulder portion extends from the case wall and has an angle of approximately 40° relative to the central axis. A neck portion extends from the shoulder portion and has a mouth sized to receive a .375 caliber (9.5 mm) projectile.