Well I finally hada chance to shoot the 50 cal Silver Hawken I got about a month or so ago. After having some firing issues with the nipple and replacing it, I started shooting 250 gr REAL bullets and PRB along with different powders (Pyro P & RS and Goex FFg and FFFg).
Turns out the rifle likes 80 gr of Pyro P with a .490 ball and .015" patches (1:48 twist). At 50 yds it was shooting cloverleafs. The REALs were all over the place.
After sighting in, I shot 6 PRBs offhand at a 6" bull at 50 yds. The rifle balanced pretty good and I managed to keep all 6 easily within the 6" (probably within 4"). Easy minute of deer.