Barrel Extension Separation!

[Wheelhorse]

In my case, the indexing pin was never in contact with the barrel threads. I have heard both that the indexing pin is supposed to go into the barrel and that it is only for indexing into the upper, not for securing the extension to the barrel.

Apparently the pin isn't always fitted into the barrel. The following quote was written by someone who seems to know something about this, found with google:
"Just to be clear, only custom made barrels will have the pin drilled into the barrel.
Production barrels use a 3/16" long pin which ONLY presses into the extension.
These barrels rely only on TORQUE to keep the extension on the receiver.
Of course, at 120-150 ft-lbs, it's not coming apart...

I specifically use a 1/4" long pin so that I can drill 1/16" into the side of the barrel, adding the pin for extra security."