I have an 1860 Colt Army by San Marco . I dug out the original box that it came in. On the end of the box is written:
Armi "San Marco" 1860 Colt Army
.44 cal. (.454 Round Ball) Percussion
use BLACK POWDER only
I have a Lee mold for .451 and .454. I use the .454 in my 1860 Colt, my 1858 Remmington & my 1858 Remmington revolving carbine. This diameter leaves a ring in all three and loads without a lot of force. 25 grs of 3f works the best in the pistols and the carbine likes 20grs of 3f I use cornmeal to fill the rest of the cylinder flush then compress with the loading lever. I try to keep them all just below the cylinder face. No grease and no wads. At 15 yards they are as accurate as any other gun I own. I can hit poker chips with the carbine at 25 yards.