John303, there was a thread on the castboolits@gunloads.com forum about converting the 1874 Gras to 45-70. Fairly detailed but every time I try to do a search for that particular set of posts I come up empty. Maybe you will have better luck. Something to think on as a regular grass bolt has a counter bore and a 45-70 case fits as though it was made for it. And don't forget these are left hand threads on the 1874 Gras actions. You could easily use trapdoor loads with no problems. I have the 1874/M80 Gras artilliary musketoon with the brass furniture and rather than a nice wall hanger it would be something neat to take hunting.Frank