That barrel does not look to have been shortened. It IS possible, given that you have a big enough Lathe, simply to chuck the BARREL into the 3-jaw, letting the ACTION rotate out in mid-air. Then you can run a REAMER in from a chuck in the Tailstock. If everything is lined-up properly, there should be no problems: the way is clear all the way from the Butt Socket to the Muzzle.
Re read your post. Got it now.




















































