50 each factory new WINCHESTER unprimed 257 Roberts +P brass rifle cases.
WINCHESTER item #WSC257PU
SAAMI maximum pressure for 257 Roberts is 54,000 PSI. Max PSI in +P is 58,000 PSI (modern rifles only). Brass specifications are the same for 257 Roberts and 257 Roberts +P. Never approach +P pressures in early rifled actions rebarreled or rechambered in 257 Roberts.
257 Roberts history: Ned Roberts experimented with necking down 7 mm Mauser in the 1920’s, Remington standardized the 257 Roberts cartridge in 1934 and the deer hunters of the time had easy access to one of the great deer cartridges of that era. Key advantages are lightweight rifles with minimal recoil. Medium to slow burning powders provide the best accuracy.
Brass case mouths MAY not be perfectly round from the manufacturing process, this can be corrected by running brass through the size die (always recommended) prior to loading. Residue from the annealing process may leave a stain on the case neck that can be removed by tumbling. Annealing involves rapid heating then cooling to impart the shell cases with the proper hardness to securely hold bullets in place and provides flexibility to expand and contract through multiple firings handloaders expect.