Thanks guys for the replies. I'm thinking hard about a 12 bore on the first one for simplicity's sake. No extractor to change. There's an outfit in Oregon that normally makes muzzleloader barrels but will make a rifle barrel from 4140 for me. I just need to decide whether I want to make it for round balls or or conicals and what to use for a twist and rifling depth. Round balls would take a 1 in 100 inch twist, I'm not sure how much twist for a heavy conical. Accurate Molds makes a nice looking 850 grain that would be a serious thumper.