Re: jc higgin 12ga
Machining for choke tubes requires much more than just the "tap". It, also, requires the proper stepped reamer. The bore will need to be measured to .001 of an inch, so a bore gauge is needed, too. Not all shotgun barrels can be threaded for tubes. O.D. and I.D. must fall between set perameters so as the shot column/wad can clear the I.D. of the choke tube 'skirt' and there remains enough wall thickness for the threading to be correct (100% thread). All in all, we're talking $400+ for the measuring tools, cutting tools and don't forget the pilots for those cutting tools. The "step reaming" is best accomplished on a lathe, which opens a whole new "can of worms". Turning the tap is best accomplished by hand, with the appropriate tap wrench (another $50 or so) not a Cresent wrench. Now, add another $16-$18 for a gallon of Ridgid Dark Threading Oil and it should become obvious why this isn't a "home gunsmithing task".
"Shoots real good!": definition; it didn't blow-up in my face. 1993 graduate Montgomery Community College 2yr. gunsmithing program