The variation in the length of the cases is due to variations in pressure and, possibly, brass hardness, from cartridge to cartridge. It doesn't help that the factory 257 Roberts loadings are often very mild. In theory, you just have to fire your factory case and then reload your perfectly formed AI case but this isn't always the way it works; except with the rimmed cartridges. Rimless cartridges often tend to shorten up so that the fire-formed case may be short in the headspace dimension. By the way, you don't need to bump the shoulder unless the cases chamber snugly. GD
