Here's the deal guys,
I installed a PWS stock tube and Vltor stock on a friend's rifle.  He supplied the parts.  Everything went together fine.  At the range, the bolt completely locked up in the closed position.  With some effort I was able to get it free and something was clearly binding in the bolt/carrier/recoil assy. I took the buffer and recoil spring out...and look what I found.  Now I dont think this came from PWS.  I certainly did NOT install it into the stock tube.  However, my buddy also swears he didnt insert it into the rifle either.  So what say you guys?  Looks like one of those bogus "recoil reducers" sold in the 90's in the back of all the gun rags.
BTW I removed this little sucker and the rifle ran like a champ, 200 rds no isses.

Well looking at this, maybe it was in there from PWS...

PWS buffer thingy

Claims to reduce recoil by 10%...it actually reduced recoil by 100%...the rifle wouldn't even fire.

You may be correct on what that is.  It may not have been in correctly.  Since neither of you new it was in there it could have backed off the back and the spring may not have been in it evenly.  Idk for sure but possible.  

Check to make sure the carrier key is not bottoming out on the ring of the lower receiver where the extension screws into.  Split the upper and lower, pull the bcg and then push it down the extension and see where the bcg stops with the spring and buffer in the extension.  That piece will have changed the depth of the extension.  Look at the ring and the back of the carrier key too for the finish to rubbed off in a rectangular shape.  It may be referenced by some that the bolt face should be up to a 1/4" ahead of the rear of the ejection port but that really doesn't matter as long as the bcg isn't bottoming out on the receiver.

tube has a consumer notice on it here ya go:

http://primaryweapons.com/store/pc/viewContent.asp?idpage=40