Last week I posted the results of my  problem with my new upper...FTFand FTEj. I isolated the cause of the malfunction to the bolt catch. No pressure from the spring. I hadn't removed the bolt catch so I thought that the spring either launched or broke. Last night I finally got around to removing the bolt catch.

What I found was a stuck detent. The perimeter of the hole into which the detent is retained was peened. This condition did not allow the detent to project far enough to engage the bolt catch. It was flush with the metal of the receiver. I used a pocket knife to remove the peened material, thereby launching the detent into orbit...along with the spring. Found both parts however. I beveled the edges of the detent hole. Shot some Tetra grease into the hole and smeared some on the spring and detent. Put the bolt catch back in place and re-assembled the rifle. Ok, off to the range.

Loaded 3 rounds into the same mag I used before. Sighted down range at the 50yrd. target and touched one off. Then the 2nd, then the 3rd. Whoopee everything functioned perfectly. Looked thru my spotting scope and damn near fell off my seat. 3 shots that looked like one hole. Was using XM193. So I loaded up 5 in the mag. Figured I wouldn't get a group like that again. I was right. Still got about a 1" group with the iron sights. Tried Q3131A. Fed and ejected perfectly. Not as accurate as the XM193.
Time to play. Had some PMC dated 1979 so I loaded up the 15 rounds and had at it. Whoo hoo. Fed through the rifle like crap through a goose. Then fired some reloads. Same result. Soooo...apparently as the rifle had been fired, the action of the bolt carrier overiding the bolt catch had caused it to peen the lower portion of the detent hole. This is an Olympic cast lower. Probably the material is not as hard as a forged receiver. I am going to build a new lower using a forged receiver next month. One thing I am going to do is slightly bevel the bolt catch detent hole. Hopefully this will prevent this from happening again. Anybody ever have this happen to them or is this a new one?

I have an ar pistol that I had to put a stiffer spring in to keep the bolt catch from bounce up from the recoil and causing problems.