Here's something I posted using epoxy putty to make an internal thread plug. Did basically what you suggested, lubed the inside with LPS 1 lubricant, mixed up the epoxy putty, mashed it in and unscrewed it. Easy peasy, no issues at all.I have an old Pieper Rolling block rifle action that I want to put a barrel on. I have no original barrel. I am thinking of putting an N0. 4 Lee-Enfield barrel on it. Cut it short, turn it down thread it and rechamber it for 32 S&W Long. Bullet diameters are the same. Problem is I am not sure what the OD of the threads should be. How does one go about measuring the threads on an ID of a hole less than 1" diameter? I don't think the three wire system will work.