If is was locking to the rear, then stopped locking to the rear the carrier key is immediately suspect.
Try a known good carrier.
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If is was locking to the rear, then stopped locking to the rear the carrier key is immediately suspect.
Try a known good carrier.
Here's an update (still haven't resolved the issue)
I borrowed my friend's AR (Double Star lower, CMMG LPK, BCM midlength upper), and his would not lock back either with American Eagle. I got some Federal XM193 5.56, and this would not lock back either gun. Again, applying slight upward pressure to the magazine would lock it back every time on both guns. I tried 10 different PMAGS and all have the same results.
I really have no clue what it is at this point... either two (nearly brand new) guns are having issues, or 10 PMAGS have gone bad... both are hard to believe.
Note to self: never ask scottryan anything because he's clearly an elitist who contributes nothing to the actual question asked.
Here is what I want to know. Did you put his upper on your lower? If you did and it still didn't work, then I suspect your lower is out of spec.
I also recommend that you try some different mags just in case. In order to isolate the problem you need to get an AR that is known to function. Then you can swap items over, like the BCG, lower, etc...
In addition you really need to try and make your post(s) clearer.
For example- You could say;
I took the upper from my friends AR and placed it onto my lower. Using xxx ammo and xxx magazines weapon would still not lock back.
I then took my upper and placed it onto xxxx lower and using xxx ammo and mags the following happened.
The same would go for using the BC from each weapon. This will help to isolate the problem.
It makes it easier for use to follow what's going on.
I know that I am going to hurt some feelings here, but I suspect that the problem is a combination of parts that make up the Franken AR.
I know that will sound "elitist" but I have put together alot of AR's and have never experienced the kind of stuff I read here on an almost daily basis.
I had the same thing happen on 4 of 5 Pmags this weekend on a 6920. The last round wouldn't lock the BCG to the rear. I planned on shooting 10 mags that range session. The 5 USGI type D&H mags I brought along, all locked to the rear. Guess it's time to retire those 4 mags, which are about 3 years old.
I struggled with the same problem. Todd has the most likely answer. But if swapping out the bolt carrier with one known to function properly doesn't solve the problem, check the gas block for proper sealing and especially proper alignment. Misalignment due to improperly drilled FSB taper pin holes (by an incompetent third party) in an otherwise perfectly good Noveske barrel turned out to be my problem.
I might have missed it, but have you tried mags that were NOT PMAGs?
I no longer own any because I've had numerous that would not hold the bolt open on the last round (new mags), as well as other issues that this thread isn't about.
If you have not yet done so, try a standard USGI mag that is known to work in other guns. Eliminate the mags as a variable, if you haven't done so already.
The magazines are the only variable I have not eliminated. I will try to pick up other mags today and see the results. After hearing other people have had this issue with PMAGS, it's starting to sound like they are in fact the issue. I'll post results after I can pick up a couple different mags (hopefully I can track down some USGI ones locally today).