.257 Ackley Improved Load Data

Caliber Overview

The .257 Roberts Ackley Improved is a wildcat cartridge created by P.O. Ackley by "fire-forming" the .257 Roberts case: the body taper is reduced and the shoulder sharpened to a 40-degree angle, increasing powder capacity while letting you fire factory .257 Roberts ammo in the improved chamber to form brass. It fires .257-inch (6.5 mm) bullets, typically 75–120 grains, and gains roughly 100–150 fps over the parent Roberts, putting it close to .25-06 performance from a shorter case. Valued as a flat-shooting, mild-recoiling deer and varmint round, it remains a handloader's cartridge, as factory ammunition and brass are not commercially standardized.