Hi,
A while ago I posted that I had a problem with a round failing to feed while the spent casing was failing to extract. Most problems seemed to have went away when I stopped using one mag in particular, and switched from regular Winchester ammo to Q3131A or M855. However, the problem has reared its ugly head again.
I have a 16" Bushmaster barrel on a -A3 flattop. I've used Brit and USGI mags. At the range, I don't seem to have the problem very often. However, at carbine matches, the first round jams, and I end up (the first rifle stage of the day) losing points clearing, or transitioning to pistol. I shoot Q3131A exclusively. I have perhaps 500 rounds through the gun now.
When I load, I load from the bolt to the rear, and firmly seat the magazine. I then release the bolt. When I fire, the first round of the first stage doesn't extract...it's like the extractor grabbed the case, and pulled it mostly out, but the spent case isn't ejecting. The bolt carrier is almost all the way back (or sometimes is all the way back), and a new fresh round is out of the feed lips, and either on its way into the empty chamber, or in partially. Sometimes the spent case is above the bolt. The only unusual marks on the spent case may be a dent from the bolt trying to go forward on it.
I know that aside from mags, I could check the chamber (to see if it is rough), check the carrier key, and check the extractor. Honestly, I don't know what rough would look like (aside from a large gouge in the metal--which I don't have). I have access to a smith if necessary, but prefer to know more about my gun and why it doesn't work.
After the initial failure, and clearing, I can shoot the rest of the day with no more problems. But, because of potential failure on the first round, this rifle will not be a SHTF gun anytime soon.
Thanks,
-Zmeja