The inserts are .745 and the threaded collar we solder on has a .750 ID..
Thus who ever bored it out only left .005" of material.. plus the solder bead.
Get a brass insert and solder it into the barrel. then slide the collar on and solder that to the insert. Epoxy will also work with this method.
Bore out the threaded collar to 13/16 and solder it to the barrel.. You will need to deepen the freak bore for the lost material.