While firing, the round attempted to chamber, but the nose of the bullet hit the barrel extension just to the left of the chamber hole causing the BCG to stop moving forward. Locked the bolt to the rear, dropped the mag, bullet fell out.
The upper is an LMT 10.5" with Colt M16 BCG. Mags are Labelle w/Magpul followers and SAW red springs. The mags are probably 3 years old with 4000 - 6000 rounds on a group of 10 mags.
I’m guessing mag issue such as spread feed lips. Any other guesses?
What about your feed ramps? Anything going on there?
It’s funny that you mention that because when I was cleaning it up tonight I noticed a good-sized “burr” on the inside edge of the left feedramp. I chambered a few rounds and the “burr” digs a nasty gouge in the nose of the bullet. I’m not sure it would cause the failure I had, though, as the bullet passed the feedramps and hit the extension wall. Unless, of course, the bullet deflected off the burr and moved upward and to the left.
I’d also measure the buffer spring. Could be a bad mag or mag spring, but it works as a ‘system’ with the buffer spring.
The buffer spring is 10 1/4".
That’s on the lower edge of the spectrum for CAR length which is 10 1/16"-11 1/4" You may want to also try a heavier buffer as well. New LWRC rifles with CAR stocks are shipping with H2 bufffers now. (4.57oz)