Showed up at a match today with my 14.5" upper on my lower off of my BM 20". That lower has a match trigger in it and is all BM other than the trigger and hammer. Had five malfunctions in 40 rounds fired. Empty case is stove piped with a round trying to chamber wedged under it. Bitch to clear. That same upper runs fine on its usual lower that has a Colt A1 stock, buffer, tube and spring. So what's the difference in full length buffers and springs? I don't have a scale to accurately weigh them.

The extractor and ejector look and move fine.

Help!

Did you check the carrier key . Maybe it's loose.

BTW . The buffer tube and spring length wouldn't be the problem. The type stock you us  dictates what buffer tube and spring length you need. The shorter stocks us the shorter springs and buffer.

Carrier key is tight. Everything looks OK. Several guys who saw it said they had the same malf in their shorty full-autos. They said it's related to carrier speed. That's why I'm blaming the buffer and spring.

Extractor is dropping the case on the way back, leaving the spend case in the action when the car upper is used on the A-2 lower.


Change out the extractor spring to a M-4 (black inset) or an extra power Wolff spring.   If you just want a temp fix, install a D-fender.  The problem will go away when using this combo.

IB,

Put the upper back on its original lower and shoot it again with the same ammo. Report back.

Took everything apart yesterday. There is no real difference in the buffers and springs. The only thing I did find was some brass shavings in the ejector hole. Maybe the ejector was being a little sticky. Won't get to shoot it again for two weeks.

Black insert is present in the extractor spring. I'm going to order some of the Wolff extractor spring to add as well.