The Marlin 1895 is a very strong rifle and will handle loads that are heavier than you'll want to shoot. I believe it has Ballard rifling instead of micro-groove so will shoot lead bullets as well as jacketed. Yes, it uses large rifle primers.
I did a little testing with Tralboss in the .38 special. I loaded some 125 grain lead for my daughter who doesn't like recoil. I also loaded some 158 grain plated with 5, 5.2, 5.4 and 5.6 grains. Velocities were 627, 727, 781 and 866. All loads were shot out of a 6" S&W model 14.
I have several .45/70s and like the caliber. I just loaded some light loads for use in the trapdoor. The Sharps shoots heavier loads and some of the 1886 loads are not pleasant to shoot. The cartridge can be loaded from very light to just shy of the .458 Winchester. It is very dependent on what...
I have a heavy barrel model 41. It's very accurate and has never jammed. Can't you rent one at a place like MFS or Manchester Firing Line? If you can't find any place closer, you can shoot mine at Harvard.
I've had the open top out twice now and shot loads with Unique, Trailboss and black powder. So far Trailboss is the winner but it's a good shooter with everything I've tried. I'll try some BE-86 and use that if it shoots as well as Trailboss only because I have a lot of it.