I got even, not doughgnut, but FAST opening patterns out of a Pedersoli .50 with shallow 1:48" rifling, with an effective range for individual animals/birds of maybe 10-15yds, depending on game size. I used a paper cartridge just tied off between powder & shot, wax/grease lubed over the shot portion, with ~3/4oz of #7.5 shot over a smaller volume (can't recall how much) of FFFg. Standard bite-tear-pour/insert-ram loading technique, and the rifling slit the paper longitudinally on the edges of the lands on firing, so they opened cleanly & reliably. I don't recall seeing any sign of leading in the bore afterwards. I strongly suspect a slower rifling pitch would add somewhat to the effective range, but I'd be surprised if you could get more than 15yds effective range on a squirrel with reasonable shot charges.
Regards,
Joel
p.s. Can one get spell-checking on posts/replies? My typing's atrocious and I often see what I meant, not what I typed, when checking.