I can’t remember when I had last seen it… Not for at least 15 years. So long, I didn’t even think it an issue. Like Small Pox, I thought it had been cured.
We had an AR-15 at the range that was having problems. We looked at everything and we finally found the cause.
A loose gas key.
This was a S&W M&P15. And the Gas Key was not staked. It had worked loose and was causing every issue you can think of. It was the last thing we looked at. The bloody Gas Key. Huh.
Had to deal with an M&P15 short-stroke problem several years ago that turned out to have a half-size gas port in the barrel.
That was a fun day.