Yeah- the one I can't figure out how to do, is to have progressive depth rifling, with constant bore diameter, with rifling .011" to .012" deep at the breech and .003" at the muzzle, even in the short barrels along with the 32" and the 39".
The Brits started this with their hollow based slug guns of the 1850's, the Enfields, and the US war department followed suit in their rifles. As far as I know, only the Iralian replica of the Enfields follow the progressive depth rifling as does my Armi San Polo Musketoon.
BTW- I split the topic due to the change in topic, what I considered a good topic in itself, one about internal chokes and tapers.