Talk about lucky, I guess - a 4th above the follower, after taking last shot of a carbine stage, the gun goes half into battery, and locks up. When we pulled the round out, this is what it looked like: 2 quarish indents at 90 degrees to eachother:
The nose was not deformed at all. The round DID feed on its own.
Thoughts? Someone mentioned he had a problem with his feed ramps. My gun is a Colt M4gery, built mid-2004 I imagine. My mags are VERY old, ex-GI, and at the range once I had one let loose a round just from slapping it in. I don't know if this information is relevant to the failure.
Here is a picture of my feed ramps:
The round failed feeding from the right side of the mag, with 3 more under it.
After the match, I unloaded another mag (different magazine) and the problem did not repeat.
Any thoughts on diagnosing these problems?
Thanks for the help,
Side dent is when the bolt was coming back to cycle, but since the top round did not get pushed down (top round wedged the round below it into the side of the mag), it got dented from the bolt lug on the way back.
Dent on the top was caused when the bolt went over/past the rim, stripped the round out of the mag from the center of the case, and jammed the round into the chamber (with the bolt at rest on the case sidewall).
Just thinking off the top of my head,
If you're not using USGI mags, now would be a good time to get a few. As for the old mags, pull them apart and clean them, remembering to check the springs and feed lips (back edge at the U channel, and welds) to confirm that the mags are still in serviceable condition.
P.S. Best guess on the shiney dent is where you used something to wedge the round out of the rifle, or the placement of where the case wedged against the second to top round.
Weak worn out mag spring coupled possibly with a black follower allowed a bolt over base failure. The mag that let a round loose when you inserted the mag probably has worn out feed lips. New mags are pretty reasonble now days, pick up some D&H or OKay (whatever they are called now, NMTG or something other) mags with green followers and you should be good to go.
If you want to salvage the mag, a good cleaning, replacing the spring, and/or green follower should do the trick.