The actual final shape is going to have a 7" re-enforced breech section whose outer dia is the same as the muzzle ring.It'll have a bladed front sight as well, which was also used on quite a few historic pieces as well. There's actually quite a few medieval muzzle loaders that are more or less constant dia down the length. I kind of bastardized several different designs into one, though. I pretty love them all, so I took the barrel contour of some of the breech-loading designs, but kept it strictly muzzle loading. I had a 24" tube to work with and my machinist buddy could only do a through-hole. I wanted to retain as much barrel length as possible, so i made my powder chamber 1.125" dia x 1.5" long and kept ~20 of actual barrel length...gotta keep those golfballs accurate!
For a historically accurate, yes, this one would have had about a 6" x 3/4" powder chamber or so, with the breech being smaller overall dia. Since I opened up the chamber dia, I had to keep wall thickness thicker and thus the built up breech. I want to mess around with "machined-rifled" projectiles (like this:http://www.defensereview.com/1_31_2004/FRAG%2012.pdf , but without the explosive round) with higher velocities and fun stuff like that was the reason for wanting the extra barrel length. I love medieval designs, though so I went with the historic carraige and wrought banding.
My favorite is a Maximillian cannon that I'm *still* trying to get a Swiss museum to respond to emails over. It has an octagonal, 8" thick breech that tapers over 56" to the muzzle that's ~3.5". No banding though. There's a pic of it in Dudley Pope's "Guns". I'll have to stop by Mike and Tracy's though to rifle it, though.
