I am just getting bits together now to make the barrel adapter, muzzle brake and choke tube. I have some old Chevy axles that are just the right size and tough steel. I have read that they are at least 1040 and possibly 4140. Regardless, they are a lot tougher than the barrel I will be putting this onto. I had to anneal the steel and it is still tough.
I have been thinking about using a choked gun in the future and cut the rifling from the muzzle. A modified or possibly even improved cylinder choke should have the right bore diameter and enough wall thickness to rifle if the choke is machined. I have a couple of guns with swaged chokes and I doubt there is enough barrel wall at the muzzle to allow for rifling. My Browning fixed choke barrel has a nice long machined choke and thick barrel walls. It is not a candidate for rifling though!
It might be a bit tricky to rifle and not start cutting the full bore walls though unless the choke is fairly tight to allow deep enough rifling and a bit of a gap to the full bore.
First, I have to machine all the bits then rifle a choke tube to try this.
Again, the goal being something I cannot buy which is deep slow twist rifling suited to round balls and full bore "square" slugs.
I have to turn my cutter head down form 3/4" pipe ID to suit a bore of about 0.700" to maybe 0.710" then reset the cutter. I just need more time! Work gets in the way but I need the paycheck too.
Longbow