A nitro-for-black load for the .45/60 Winchester would suffice for a smokeless load, I am sure.

The .45/60 case is 1.9" & shot normally bullets from 260gr. to about 340gr. when handloaded - (merely an assumption of mine due to the 340/350gr. bullets available for the .45/75 ctg.)

I'll get my brothers data for his Winchester M1876 .45/60 rifle, with which we worked up loads to include 345gr. bullets - BP equivalent in TB, H4198 and IMR3031 as well as full power with 4198 and 3031 powders for that weak action'd lever gun.

The best, most accurate loads in it were the cast 300's and 345's at around 1,800fps, but it shot reasonably well down in the 1,200fps to 1,300fps range was well.

Trail Boss actually shot fairly well, however was VERY slow.

I'll attempt to get that data today- have to go over there to deliver his new fly rod.

I suspect a BP load in that Westley Richards might make around 1,150fps to 1,200fps with a 380gr.bullet - maybe 1,250fps with C&H #6 rifle powder. The equivalent would be a case full of Swiss 1 1/2.