The gun is set up for saboted rounds. There are a lot of options out there. The most common are 250-260 grain loads traveling at from 1600 to 1900 FPS depending on what literature you read.

Plenty of other options out there, up to a 3 1/2 inch monster that the Hastings people make. Not all of them are for rifled barrels but a lot are.

A 260 grain bullet at 1600=1900 FPS is about the same as the original 45-70 load with the 405 grain bullet at about 1200-1300 FPS.

What would be interesting with this gun, sense it has a adjustable regulation system and you can be sure it's plenty strong, is to get brass shells and load full sized bullets in it........