Depends on your temps and how long you cook things, but Varget is a terrible choice in the 223 as far as temperature stability goes. The original choice H335/Bl-c(2) are very good choices. Being that 748 came from that family with some added copper cleaners, and the fact it was the Benchrest choice for a long time, is try that as well.

Also, not sure if those bullets are the AMP jacket or not... But it's possible is an RPM issue.