SJ,
Welcome to the forum. I would not recommend using Buffalo Bore ammunition in a modern '73 .45 Colt but one can load ammunition to a bit more velocity than the current factory standard cartridges.
Certainly a 250 gr bullet at 1,200-1,300 fps is a ok using slower powders and would be similar in performance, although a bit more powerful due to the heavier bullet, to the vintage .44-40 which accounted for thousands of game back in the day......
w44wcf