So, not to belabour the point, and draw undue attention to my hair-brained idea, I micrometered some bullets. The .454 'Cowboy' bullets measure mostly .4545, while my 45/70 bullets (.458 dia. on the box - both the Sierra 400 gr. and the Hornady 325 gr. FTX Leverevolution bullets) actually measure .457. Both these bullets are copper clad. That's a difference of only 2.5 thousandths. Without slugging the bore (to see what my 1895 barrel actually measures) I wonder how much of a problem these slightly undersized bullets may actually present. Will the fact that they are a soft cast bullet allow them to deform somewhat under chamber pressure to make a better seal, or will hot gasses simply blast on by them melting the lead for deposition in the barrel? It's kind of like the guys who use .308 caliber bullets in their 7.62x39 (.310") or their .303 British (.311") loads perhaps? Is this worth a try?