For a factory load I think it's hard to beat the PMC .45-70 +p+ loaded with the Hornady 350 grain Flat Nose Soft Point. They leave the muzzle at 2025 fps for a muzzle energy of 3167 ft/lbs. If you load your own there are many options like the Swift A-Frame and Trophy Bonded Bear Claw and Speer. I shoot a custom siamese mauser, but I used to have a guide gun. Be sure to check your overall length. Not just your data, but functioning and feeding through your rifle. I had a few problems with longer loadings not feeding from the tubular magazine up into the chamber. Had to drop the lever out and remove the bolt to finally clear it. They loaded into the magazine fine too.