Starline Brass Star4570EUP5: Our .45-70 brass has been tested at elevated pressures suitable for Magnum Heavy Hunting Loads in adequate gun systems. When loading with black powder, annealing of mouth may be necessary to allow case to properly seal chamber due to lower pressures generated by these loads. Starline\'s case is produced very strong to withstand high pressure loads associated with smokeless hunting loads and since the only way to make brass harder is to work the material our only option is to leave them stiffer so the customers can anneal for specific application.