WTF! Got a new AR upper and none of my mags will fit!

[shibbershabber]

Just picked up a new A2 upper and when I assembled it, the mags wont fit.

I have a known good upper and lower that I have fired many times... so out of 3 lowers and 2 uppers being put together in all combinations, I have determined that the new upper is the problem


The mags fit into the lower no problem, all mags the same. But then the new upper is locked in place, the mags dont go in all the way, if I force them they will stay but do not click into place at all. I mic'd the width of the uppers and they both seem the same but with one upper assembled everthing is fine, when i put the other one in... mags dont go.

Even removed the bolt from the new upper and I have the same result. Anyone seen this before? I am unsure if I can take it back to the guy at the gunshow... is this something that I can dremel into submission?


thanks!

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[Bigbaddude]

I had the same problem years back. I fix the problem by lubeing the crap out the upper and the problem went away. Now the mags go in nice and smooth and I don't have to smack them on the bottom to get them to lock in.
I am no AR expert but it work for me
Good luck.

 

[Modly]

If you pull the bolt back, and lock it with the catch, do the mags fit?

 

[shibbershabber]

yeah I took the bolt out completely and still had the same result.

 

[KalamaMark]

You might want to check your gas key for proper staking, too.

I had a 'gun show upper' that shook the gas key loose on the second magazine.

Did ya try and lock an empty mag in the lower while the upper was separated on the front pivot, then try and close it? I'd try that with no bolt, bolt in place, then with a full mag. This should give you hints on where your interference is and how to fix it.

"I am my own warranty provider"

 

[shibbershabber]

Yeah the mags lock in fine with the upper off...

I will fire it before doing anything more to it. At least I could try and file the mag catch so that it locks the mag in 'shallower'... but if it works I can tolerate the lack of clicking

 

[rick benjamin]

Don't file on your lower, Your new A2 upper is the issue.
Use some machinest's "DYKEM BLUE", to show the high spots in your upper.

 

[Modly]

Do you have a pair of dial calipers handy by chance?

 

[shibbershabber]

I was thinking of filing the mag catch itself, that way if it didnt work Id only be out a few bucks. I never intended to take any meat off of the receiver.


Modly, yes I do.

 

[Modly]

I've attached two photos with my calipers inside of my upper. At the bolt, the slot is .810" wide, and at the rail it's .925" wide. I would measure these things on your upper to see if there is interference. If the slot is too tight, the mag won't fit. Mine is super loose, but you'll need at least .885" of width on the rail to fit a mag.

 

[Kram Chrome]

Try closing the upper on your lower with a mag installed. I think the maker forgot to put a relief cut for the mags to clear. I will post a pic of my upper so you can compare.