Potential problem with Anderson receiver

**Esq.** · 07-27-19, 12:01

Thus last week we were on vacation to a family reunion. As part of the gathering several of us had some range time. One of my cousins had a rifle he built on an Anderson lower. The upper was a Psa....

As he was shooting the rifle it would drop the magazine. I checked to be sure he was fully seating it and it was initially locking up-not the problem. He would fire a round and the mag would drop out. The gun fired and ejected perfectly when the mag was properly sested.

Thinking it might be a bad mag I tried several USGI Aluminum mags...it would do it with some Centers and Okays and an FN I had along. It would not do it with a few Centers, a Bushmaster or any Pmags. Thinking it could be a mag catch issue I pulled the one from my personal gun....same problem.

I'm thinking it has to be a receiver tolerance issue?

**gaijin** · 07-27-19, 12:54

Or a marginal mag release. Might switch out with a different, vetted release and see if issue continues.
Right hand shooter, not coming in contact with release inadvertently?

**Esq.** · 07-27-19, 13:54

Originally Posted by gaijin

Or a marginal mag release. Might switch out with a different, vetted release and see if issue continues.
Right hand shooter, not coming in contact with release inadvertently?

Yea, I did that. I had my go to rifle there, a DD v5 and I swapped in my mag release for two mags worth. Same crap. Gun did the same thing regardless of who fired it.....Out of spec. receiver is all I can think of.

**bamashooter** · 07-27-19, 14:16

Has the problematic lower been tried with a known good upper?

**Esq.** · 07-27-19, 14:25

Originally Posted by bamashooter

Has the problematic lower been tried with a known good upper?

No. Hadn't thought of that as a potential issue....

**bamashooter** · 07-27-19, 15:27

Originally Posted by Esq.

No. Hadn't thought of that as a potential issue....

Nor have I however, when researching this problem, I found this to be interesting: "Hence to first make sure that the upper receiver area above the top of the lower front mag well area is not protruding over the top of lower edge, and preventing you from being able to lock a mag home to begin with, then to see the amount that the bolt catch tab is protruding into the mag well as well."

"Lastly, when you fully load a mag, it fully loaded when the top round can be pushed at least 2/3 of the way down to almost allow an other round. If you are loading the mag, to the point that once the last round is loaded, that top round can not be pushed down at least 1/2 of the way of allowing another round to be added, the you putting too many rounds in the mag. Hence on mag lock up to a closed bolt, the entire round stack has to be compressed downward in the mag (against the bottom of the carrier), and if too many rounds in the mag, the stack can not compress/the mag is not going to lock home."

Hopefully, it's ok link to another forum. Here's the complete deal with photo: https://www.ar15.com/forums/AR-15/Ma...ut-/66-726809/

**Esq.** · 07-27-19, 15:44

He only loads to 28 rounds so it's not the second issue. I'll have him try another upper just to rule that out. He has a Walmart closeout Colt 6920 that he bought several years ago. This gun was going to be his "backup" to the Colt.