I have thought about the paper patch idea in my 38-55 for making a 375 whisper to shoot big bullets sub sonic. My line of thinking is big thump low noise ...just different and fun. Never really thought about it in terms of shooting max loads. There is bound to be a mould maker somewhere that would make what you wanted in the proper size in a gas checked bullet. A gas checked lead bullet could be shot very fast with little or no leading.