I found an great new target load for my Browning High wall. I used 25 grains of 2400 with a 350 grain mangnus cast bullet. Consistantly grouped all holes touching at 50 yards. I don't have a chornography so I cannot speak to the speed. There was only very mild leading that was easly cleaned after 15 rounds.
I have no idea on gunsmithing questions. You will have to take that up with someone at a higher pay grade. You might can buy a 45-70 and have it reemed out to 45-100. I don't know.
LongDistanceOperator- Sure it can!! The Hiwall can take anything you can put into it, pressure-wise. About the only limitation MOGHT BE cartridge length, but the .45/110 or .45/120 shouldn't be too long.