No, sorry for not being clear. Black powder is fun and worth messing with but I was just talking about black powder velocity. You can look on the load charts for loads that are safe for a trapdoor and start with those.Are you suggesting I use BP for my loads in the beggining or load the equivelent of what the PB load was. How do you find out what the velosity was on the BP loads of the day. I have heard that around 1200 to 1400 was the norm. Seams slow but it is pushing a huge bullet.
It there a conversion chart out there some where that will give you the info I am looking for. I did see a reloading pamphlet at Cabelas that has just the loading info for the 45/70. Wonder if that is a worthwhile thing to have.