I am not an expert on QuickLoad and would like to validate my findings with someone else who has more experience.

I have a 45-120 case at 3.25 inches. water capacity 127.6 gr.
0.458 cal. Rimrock 350 gr cast bullet with a length of 0.891
56 gr. IMR-4198 powder
COL at 3.671 in. which gives a seating depth of 0.471 in.

Can you tell me what pressure and velocity you get from a 26 in. barrel?

Thank you,
Eric

If you are using is 56 grains of 4198, you would be better off with a 45-70. You will have a huge air space in there, which is usually a bad thing. 45-120s were made for use with black powder and 550 grain bullets.
I used to load light smokeless loads in big Sharps cartridges, but I don't use it much any more.
I can't answer your question. Guess at 2000 fps. Asking a lot from a cast bullet.

I don't have that much experience with 4198 but that load is only about 61% capacity. I would have concerns I would opt for a smaller case less powder and get the same velocity.

Pressure around 25,000 and velocity around 2000fps.

Thanks for the feedback

Eric