I have shot a few hundred cast bullets out of my 375 JDJ with ssk break.

It can be done but you have to watch the ports and make sure they do not clog up with lead and lube. it they do clog up and you fire a round the pressure will blow the lead/lube out at high speed and can injure you and other people around. A pipe cleaner that fits in the ports should be taken with you shooing and ran trough with a lead remover about every 10 rounds or so