My Marlin 336 in .44 Magnum (a 1964 vintage gun), as well as my son's octogon barreled 1894 both have .432" groove dia. barrels. I slugged and measured them both. A lot of testing showed me that any lead alloy bullet, gas checked or not, needed to be at least .432" dia or it wouldn't group at all...ie. 5-6" gps at 50 yds. Properly sized (.432" gas checked home cast bullets) did much better. With either gun, scoped with a little 2.5x Leupold Alaskan, Lyman's #432215gc bullet, cast from wheel weights and sized .432" will keep 5 shots in less than an inch and a quarter. Don't know what Winchester, or Rossi measure, but our two Marlins take larger dia. cast bullets. Standard, jacketed bullets from Remington, Winchester and Hornady that measure .429-.430" do as well as the larger lead alloy ones.
HTH's Rod