I used a pipe thread cutter to remove a 1/2" long barrel shroud from in front of the front sight post of a Saiga 7.62 x 39mm Rifle barrel, in order to thread the end of the barrel for a muzzle device. The Saiga Rifles don't come with muzzle devices, and mine didn’t have threads pre-installed, so you have to thread the end of the barrel yourself.

The muzzle device calls for a 14 x 1LH thread. When I removed the barrel shroud, the tube cutter wheel did cut into the barrel slightly deeper than the depth of the shroud itself, probably about the width of a dime.

The barrel diameter mics out as follows:
Barrel diameter =.565”
Diameter of the Tube Cutter Groove = .489”

So, the difference between the OD of the barrel diameter and the OD of the groove diameter = .076”

A 14mm x 1 thread has a .497” (thread minor diameter), so when you factor-in the.489” (Tube Cutter groove diameter) that equals .008.” So, I should have about .008” of excess barrel material above the minor diameter of the threads.

So, will cutting accidentally into the barrel slightly with the tube cutter affect the integrity of the barrel?

I assume the pressures at the end of the barrel would be significantly less by the time the gases are expelled through the piston mechanism, etc. I also assume the muzzle device itself will provide quite a bit of additional strength when screwed down and completely covering the tube cutter groove. I’ll be using some Rockset to secure the muzzle device to the threads so the muzzle device doesn’t move.

You're fine. I promise - the barrels are much thicker than needed purely for safety. They're only so thick due to barrel whip.

Either you made a typo, I'm misunderstanding what you're saying, or you mathed wrong. .489" is smaller than .497" so the groove will still be there after cutting the threads.

That being said, the above poster is correct. Barrels are much thicker than needed for safety. The only thing I would be wary of is the stress riser caused by a sharp pointed v-groove like that. Even the roots of threads are rounded to reduce stress risers/concentrations. Believe it or not, machining away a little material to turn that sharp groove into a rounded groove would be better. That being said, the only time I would actually be concerned about it is if you were going to hang a heavy suppressor on the end and do some full-auto fire which would all exacerbate the various stress & fatigue issues. Just putting a brake or normal muzzle device on? Don't worry about it.