Hi..new member here. Wanted to pick some experienced loaders brains on this....
I've been loading the 45-70 and 45-90 in everything from my vintage 1886s to trapdoors and highwalls. Lately I've been using Trail Boss instead of BP, especially for hunting deer, because sometimes its hours or days before I can properly clean these old guns. I'm very happy with it, its clean, nearly as mild in pressure as BP, and produces respectably accurate loads.
Now I've recently lucked into an original 50 Express. 1886 rifle with a nearly perfect bore and internals, but the outside had been refinished. I am thinkin of sending the gun to Turnbull to be redone, and I really dont want to shoot BP in it. However, Hogdon doesnt list a load for the 50-110 in Trailboss (or anything else).
Would it be an unreasonable assumption to take a load with a similar case capacity and bullet weight, scale it back 5%, and start from there? Hogdon does list a trail boss load for one of the big sharps cases (45-120 I think). TB powder is extremely voluminous and does not have to be packed like BP, so I'm not worried about the powder charge not filling up the case.
I know there are some who will say there are no reasonable assumptions in reloading, but I thought I'd give it a try before risking damage to the gun, even though I have a lot of confidence in the strength of the 1886.