I shot the following with my GPR 54cal:
.530 RB: .18 Pillow Ticking Lehigh Valley Lube
.535 RB: .10 Ox-yoke cotton patch,Lehigh Valley Lube
I can shoot either RB /Patch combination and still achieve a 2inch group @ 100 yards, could be better, but my eyes aint to good these days. Not to much difference in Point of Impact between the two RB/Patch combo's. I also have used the homemade Moose Milk Lube with success, but like the Lehigh lube best of all. I shot over 200 rounds of each RB/Patch combination at the range, so be prepared for some long hours at the range. Good Hunting!