I hope I don't show complete ignorance in this post, but an operator induced anomily was pointed out to me with one of my AR-15's carrier. I went to a private shoot Saturday and noticed I had some short-stroking and double feeding issues with one of my rifles. The one in question is a Colt 6920 I bought at a gun show in 2004 or 2005. I don't know how many rounds it had through it before I bought it, but I have fired roughly 3,000 rds. since owning it. A few years ago it began short-stroking and the problem seemed to be solved after changing the gas rings on the bolt. Since then, I have noticed a few of the same issues but not as bad as I had Saturday. I couldn't seem to get through 10-15 rds. without problems. A friend who was there is a Class III dealer and when he looked at my carrier, asked where the rest of it was. As you will see from the pictures, it appears that someone had machined off the lower half of the back of it. The other 5.56 rifle I own is a Knight's Armament SR-15. I honestly have to say that I did not think anything was different about the carrier from my Colt since I knew the bolt on the KAC gun was proprietary, but I knew the carriers were the same.
My assumption is that the reduced weight of the BCG is causing it to cycle too fast and not going far enough in the buffer tube. Is that correct? The buffer is an older style "H"-buffer. Was this someone's idea of making a low mass carrier at home? Everything cycled well when I ran my friend's full-auto carrier from his M-16. Sorry for the link...could not upload picture to the message for some reason.