I removed my barrel yesterday ( as I have done many times before using a DPMS claw, barrel wrench and a vise). The barrel nut may have been a little tighter than the others but I can't say for certain. Upon removing the barrel I noticed the indexing pin to be canted and upon touching it, it moved. I could also remove it without force. This ever happen to anyone else? Any idea as to what caused it? I am getting it replaced for free from the un- named company ( they are excellent and have addressed this with much vigilance so they will remain un-named). Just asking for my own information. I did nothing differently than I have done many times before.

The pin is too short, and the hole is not drilled proper...

The hole for the pin should be bored through the extension, and into the threaded portion of the barrel so that the pin effectively locks the extension to the barrel, and pin is supported proper.

I had this happen... I would reference this link from Bushmaster.  I would not dril into the barrel extension though...this pin indexes the barrel in place with the upper and is not made to to keep the extension in place.  http://www.bushmaster.com/faqnew/content_by_cat.asp?contentid=181&catid=100