[convolvatron]

haven't looked at rifling, but making single point boring cutters for a lathe isn't at all hard. you can just screw a carbide cutting insert onto any old piece of steel.

seems like you'd have stiffness problems for long barrels (?)

[dsfyu404ed]

You could make a push broach that holds an insert (or make it out of HSS then press it through the barrel.