.338 Weatherby RPM Load Data

Caliber Overview

The .338 Weatherby Rebated Precision Magnum (WBY RPM) is a modern, high-performance rifle cartridge developed by Weatherby, Inc. and standardized by SAAMI. It was introduced in 2022 as the company’s 16th cartridge and designed to deliver magnum-class ballistics in a lighter, more compact action.

Unlike many traditional belted magnum rounds, the .338 WBY RPM uses a non-belted case with a rebated rim and a 35° shoulder, derived from the 6.5 WBY RPM parent case necked up to accept a .338-caliber (8.6 mm) bullet. This gives it increased case capacity and efficient powder burn, producing high muzzle velocities and flat trajectories in lightweight rifles such as the Weatherby Mark V Backcountry series.

Factory loads typically launch 185- to 225-grain bullets around or above 2800 fps, translating to powerful energy retention suitable for large North American game like elk, moose, and bear.

The rebated rim allows use in actions with standard bolt faces while maximizing magnum performance without excessive rifle weight, making the .338 WBY RPM particularly appealing for backcountry hunters and long-range big-game shooters.