What's the difference between the two rifling systems? Have you investigated using a different allow to cast with, you didn't mention bullet hardness, either bullet gas checked or not? Just because your keeping your velocity down, doesn't mean your not going to get leading, does it?
Sorry but, you expressed a popular theory from the Internet, and I would like to know why you believe this? Mind you, I'm not saying your wrong, just want someone to convince me this is true with cold hard facts.