AR15 - Cartridge pops out of mag upon insertion.

[Kamerad]

I’ve run across a problem previously unknown to me, and I’m optimistic the collective wisdom of The Hide can help!

AR platform. BCG locked back, insert magazine firmly....top cartridge dislodges from magazine. Hit bolt release, and hello double feed! With a combination of uppers, lowers and magazines, I believe I’ve isolated a culprit. It only occurs when the PSA upper is present, but only about 25% of the time. That said, even once is too often.

My theory is that the magazine feed lip recesses in the upper receiver are just tight enough that the feed lips distort, causing the magazine follower spring pressure to push out a cartridge.

Magazines used - Lancer A5awm, Magpul Gen 3, Palmetto branded Aluminum GI (D&H?)
Uppers used- PSA, Aero Precision
Lowers used-Aero Precision, Maxim Defense

Anyone have an idea what could cause this?

 

[iktomi]

What you're describing doesn't make sense to me...

Based on the description of the malfunction, it sounds like a magazine issue (I'd be inspecting the feedlips, and verify that the top round is fully seated to the rear of the mag before insertion).

I cannot imagine how the upper is inducing the malfunction.

To rule it out, apply some kind of marking agent on the exterior of the top of the mag... (marking fluid/Sharpie on GI mag). If there's contact between the upper and the mag(s) it'll show up by wearing off the Sharpie.

If it is the upper specifically, you should see contact with the PSA that doesn't show against the Aero.

To repeat the opening sentence, what you describing doesn't make sense.

 

[Kamerad]

I like your idea of marking feedlips to verify contact with upper, I’ll try that.

I’ve already contacted PSA, waiting for a response.

Bad magazine was my first thought, so I used several, with the same outcome. Most of them were new in package.

Just so I understand you, do you mean the symptoms don’t make sense, or my description of the situation?

 

[Powder_Burns]

5.56?

 

[Kamerad]

5.56?

Yes. Nato spec 62 grain.

 

[Powder_Burns]

Don’t slam the mags in and see if that solves the issue. Are these full 30rd mags when this happens, or would a mag with 5-10 rounds do this as well? If the mag feed lips are the issue I would think you could replicate the problem by just slamming the mag onto a table.
I also think if the upper was making contact with the feed lips it would be difficult to seat a mag without some force. It shouldn’t be touching the upper.

 

[Jcmar15]

Lancer mags are known to sometimes have this problem. Try pmags or good usgi mags and it should fix your problem

 

[mark5pt56]

Feedlips and/or springs. One thing that is relative is "seating firmly" that obviously has different meanings. It should be a seat and a tug. If you have rounds popping free upon insertion or when the bolt is released, two live rounds-it's the magazine(aka SEAL Party). The only other way to get two live rounds during the feed cycle is the user monkey fucking the charging handle.

Check your magazines in case you've been beating them like a rented mule. The mag catch slot may be deformed, this may/would cause bolt drag.
Check a couple things, after seating as you do, pull down on the magazine to see if it has slight downward movement. If your mag catch slot is distorted (repeated over insertion) it will be rather noticeable.

 

[Stev0]

Don't slap the bottom of the mag.

 

[Steel head]

If you slap the ever living crap out of a lot of double feed mags they’ll often do that.
Especially if the springs are a bit weaker.
You don’t need to beat it like a red headed step child.

 

[Kamerad]

After work this morning, I sat down to re-create the symptom, using the feedback you all have offered. I’ll be damned, but nothing. Maybe I was being too aggressive on loading earlier.

Once I can get to the range later this week and live fire, I’ll keep an eye out for any funny business.

Thanks again for the feedback.

 

[Bourbon_and_Bullets]

Only time i have seen this is with weakened feed lips and full mags but never on insertion. I usually just load 28 rounds and that does the trick.

glad you were able to ID and correct.

 

[clcustom1911]

With bolt locked back, just insert the mag until the mag catch engages the magazine and use the bolt catch to releasethe both. No need to be super aggressive or knock the bottom of the mag while seating it there.

See below for a proper bolt lock reload. Mike Pannone is the shizzle of the nizzle.

 

[Triple D]

Premature ejection....

Try thinking about something other than shooting and see if that helps.

On a serious note, I’d suspect that it’s either the feedlips, the bullets not being seated far enough back or possibly an out of spec bolt catch that’s hitting a round when the mag is inserted.

 

[Kamerad]

Premature ejection....

Try thinking about something other than shooting and see if that helps.

On a serious note, I’d suspect that it’s either the feedlips, the bullets not being seated far enough back or possibly an out of spec bolt catch that’s hitting a round when the mag is inserted.