I have done very little on a lathe and want a bit of hand holding if you are game. Feel free to critique anything you do not see as correct.
I am turning a Handi 12ga Shotgun into a small garden gun in 32 S&W Long.
I have decided that the way I want to proceed is to turn the Stainless Green Mountain 19" raw 7.62" barrel https://www.gmriflebarrel.com/GMRBIt...f-8bc26e0bc27e down enough to insert from the breach of the shot barrel.
The shot barrel will be left about 12" long to the front of the handguard and cut off diagonally top being shorter.
The rifled barrel will fit firmly in the shot barrel. It may be epoxied, set screwed, or maybe just held by the interference of heated outer and cooled inner.
I would like for you to look over my shoulder and see if the machine work is going to be done in the most efficient manner, so here goes:
Barrel turning sequence to fit a rifled barrel into a 12 ga., 2-3/4” chambered Handi barrel.
Install the 19”x1.250" raw rifled barrel into the lathe.
Muzzle onto the centering tailstock and breach end in the four-jaw chuck about one inch.
Install the follow rest to support the long thin barrel. Or do I use a steady rest in the middle and turn the barrel one half at a time?
12ga chamber dimensions; http://www.dave-cushman.net/shot/shotshellloads.html
Cut the 1.250” barrel down to 0.866 for the rim of the shot shell bore.
Leave 0.250 for this rim diameter and move to the next step cut.
Cut the next step of the barrel to 0.812” for 2.740”. This should make the forward portion to the chamber step become an interference fit just before the end of the chamber.
The next step is to turn the rest of the barrel down to 0.7285 or what ever will allow the shotgun barrel to slide over the rifle barrel.
I will be able to remove the tailstock to check fit before removing the barrel from the chuck. This way I get to test fit without removing from chuck and changing things.
Once I am satisfied with the rifle to shot barrel fit, I can use a parting tool to cut the barrel off from the chuck inside the ¼” of 0.866 first turn, being sure to leave more than 0.074 for the rim thickness.
Now I can turn the barrel around, stick it into the chuck and face off the breach face to the exact length for flush fitting into the shotshell chamber and nearly zero headspace against the receiver.
Now turn the barrel around in the chuck again, to face off and crown the muzzle.