bob, i am new to this board so please be patient with my rambling, if you check you may find that the .511 /.512 marrked bullets are for loading in metalic black powder cartrages , if my memory serves me correctly. in a muzzel loader they may develop way to much preasure, thus very poor acuracy and/or danger to all around? if it were me i would check with makerof bullets, thanks for listening. good luck