Sorry my mistake I know the sizes are different and assumed that others did too. Yes you have to size down the 405 grainer and also the 400 gr Speer. the jackets are thin and will size down easily in a cast bullet sizer. Along with the cast bullets for the 458 and 45/70. The loads can be qiute powerful in a 12 inch gun. Also with relativly small charges compared to the 45/70.