These are about the simplest the tools for this job,,working on the M12 bbl extension.
If you try and go any simpler than this, you will more than likely crush or otherwise damage the bbl and bend the bbl extension.


If the old bbl extension over tightens when installed onto another bbl.
You can punch the threads on the bbl forward a slight amt. That makes the take-up of the threads a little quicker (lack of a better word)
and the extension will thread back on and come up to about the 9 oclock position in contact with the bbl shoulder.
Then the wrench will be needed to torque it into position the rest of the way.

This same method is often used to tighten a TD joint on some rifles like Winchester TD guns.
Not meant for repeated disassembly/reassembly. Meant to be assembled and left that way.
I've seen it used to tighten a bbl up on a bolt action rifle as well that is over clocked a bit.

Use a small face flat 'drift' and a hammer. Place the face of the drift against the side of the V of the thread and lightly and evenly punch the thread TOWARDS the muzzle of the bbl.
Start at one end of the thread on the bbl and go all the way around the entire thread and all the way to the end of the thread.
It doesn't tke all that long. But the threads are small and fine. Take the time to do it right and don't mess the threads up.

You are displacing the V a very few .000 forward. That draws the part being screwed into place (the bbl extension in this case) onto the bbl 'quicker than the orig threads.
As a result, the extension comes up tighter to the bbl shoulder quicker (that 9 oclock position) and then needs the wrench torque to really tighten up to the 12Oclock for you.

Many around now would just use LockTite or similar I assume and save the work. But I really don't care for the stuff.


If the old extension comes up way short of where you want it to be, you can either take small amts off of the bbl shoulder that it sits against.
.. a safe edge file works well. I use a sharpie pen as high spot marker to see where I need to file.

Or you can simply remove matrl from the front side of the bbl extension. Again Sharpie mark the front of the extension and screw the bbl in tight. Remove the bbl and file the spots down where the marker is rubbed off brite (high spots)
Keep watch as you get closer to the 12oclock position where you want the bbl to end up and leave some 'crush factor' turning distance for the wrench to tighten the assembly together.
Don't go by the old witness marks.