Pitchy:
I have been reading your posts and although I do not own a 45-60 rather a 45-75, I thought that it would not be out of line to mention that Ken Waters lists, in his book, a load of 22 grains of 2400 under a 300 grain bullet for a 45-60. I use it in my 45-75 under a tuft of kapok with a 350 grain bullet and get very good results both in accuracy and in velocity. Also, I found that my rifle, being fussy that it is, likes a cast alloy of 16:1 which, incidentally is what is listed on the backs of old cartridge boxes that I have read. As far as using black powder goes, I, also, have found that my rifle likes the Swiss 1½ the best and it does clean up quite well.
So that is about all the info that I can part with being that there are two different calibers talked about here. Good luck...