If it's a Pedersoli or one of the older Shiloh or C Sharps, with the generously sized chambers or throats, then going with something .450 diameter before patching may be the best bet. As to Zepher sized bullets, the barrel twist will determine the length the gun will handle if you go to shooting past 200 yards. Way back in the late 70's early 80's we had decent results in a 3 1/4 shooting the 550 grain patched bullet RCBS sells, but nothing coming close the accuracy that folks serious about paper patching today come up with.
