I don't know if there are enough heavy, high BC bullets to get very much more from all the powder and barrel wear. If you want something bigger than the 204 Ruger or 20 Practical (20-223) then you might look at the 20-250 Improved. Weaver Rifles in Colorado is playing with it now, with some custom heavy bullets and are getting some good results. I found their site by looking at some work they'd done for the Rocky Mountain Big Horn society, so I haven't shot or even seen any of their rifles. Here is a link to their site: Weaver Rifles Web
. The info about the 20-250 imp. is in the technical section.