I don't have any experience with the cartridge, but thought I'd mention that it's correctly referred to as the .45-75 Winchester. It should not be confused with the .45-75 Sharps, which is actually the .45-70 Gov. renamed by Sharps.
I don't know the twist rate of your rifle but understand the original cartridge used a 350 gr. bullet. The information I have on the cartridges say the original factory load yielded 1383 fps with a full case of BP. An alternative is 1380 fps with 24 grains of IMR 4198 smokeless. Lyman mould # 456192 is recommended. Good luck with your reloading & shooting.
Wayne