Has anyone here had any experience with the “Tension tubes” as used on “pencil-barrel” (standard) AR-15s, back in “the day”?

The idea was to machine a “perfect” radial flat surface on the front of the gas block/front sight.

Then fabricate a steel tube that has a generous clearance fit over the protruding barrel diameter. Either cut a 1/2″ x 28 thread in the end of that tube or “attach” the tube to a standard 5-slot birdcage.

The idea was to be able to wind in the “tube” onto the muzzle thread until it applied tension to the barrel. A torque wrench provided reference numbers. Test fire with the “ammo du jour”, increase the tension, rinse and repeat.

Plot the group sizes against the relevant torque settings. Pick the “best” one and do a verification group and re-zero to finish.

The catch was that there were TWO things happening here. The axial tensioning and thus changing of the relative “stiffness” of the front-end of the barrel and, the tiny radial compression applied to the very end of the bore by the thread interaction.