I've had 2 M1895 Marlon 45-70s. I would not use Ruger#1 loads in it. The theory, or at least how we thought, the 1895 was offered in 444 Marlin at one time. The SAAMI pressure of the 444 was 51,000 psi. The 45-70 is something anemic like 28,000 psi to account for trapdoor rifles. The different load levels account for 3 pressure ranges - trapdoor, Marlin 1895, bolt guns. Then the 450 Marlin came along, SAAMI pressure is 43,000 psi. My bear load was a 400 gr Speer sitting over H4198 (can't recall how many grains) at close to 2000 ft/sec. I had an Re7 load that was similar velocity.
I also tried the Horn 350 gr RN. I shot 1 bear with it and was not impressed. The 350 RN was made as a light bullet for the 458 WM and is a bit too tough constructed for 45-70, at least in my opinion. The 400 gr Speer usually exits but will make a visible impression when it hits.
One thing I'll say about loading warm 45-70 loads - you'll run out of recoil tolerance before you run into pressure issues. The drop in the 1895 stock, plus 400 grains at 2000 ft/sec is more than most people care for. We used these guns/loads when we hunted Canada for black bears. It is a very potent black bear load but it kills out both ends.
