Aero Lower tight with USGI mags

AR/M4 AR Technical Discussion
1

Bought an Aero lower, and checked mag fitment when I got home. It’s really difficult to insert and remove about half the gen 2 pmags I have. Thinking that it may be a pmag issue, I also checked it with NHMTG, Okay, and Center usgi msgs. I also experienced fitment issues with several of these 20 and 30 round usgi mags. Seems to be almost 50/50 with both pmag and aluminum mags.

Sent it to aero, and they say it’s in spec and en route back from them. Told me to just stick to the mags that work in it, and it’d loosen up with use maybe. As a point of info here, these “problem” mags work great in my bcm, Colt, and my friends Daniel Defense magwells.

Anybody here know of a decent way to open up a magwell?

And for the record, I’ll be taking mags to check fitment next time I buy stripped lowers.

2

Chalk it up to lesson learned and use it to beat on and practice with.

3

Figured that might be the end result. Lesson learned for sure.

4

If you’re going to eat the cost of the lower, you might as well try and fix it. It’s pretty easy to ascertain where they are rubbing and “fix” it. If only half the magazines are dragging, it’s not going to take much to remove the material (file or sand paper). Still could make a range beater out of it.

5

Had this problem with an Anderson. Saw where it was tight, filed and sanded a bit, done. Works great.

I know that goes through the hard anodizing, time will tell if that’s any kind of issue.

6

If it was me, I could contact them again. It can’t be “in spec” if USGI mags aren’t working. Especially if those mags work in other guns. If they won’t swap it out, sell it and get a lower that works.

7

All my gen 2 Pmags are tight in my RRA, PSA, Anderson lowers.
Had to file the Pmags. I’ve been told the newer ones are a bit smaller but Okay mags should fit in everything.
My Okay 20s drop free when empty.
Sounds like it’s time to file that magwell.

8

Had the same issue, the took it back and reworked it. Works fine now, but it’s my first and last AP lower. It’s a beater rifle anyway.

9

Aero is usually high quality, from what I’ve seen of others’ experiences, and my own. Running two Aero lowers, and one upper. All stripped, incorporated into full guns.

This whole thing reminds me, my primary carbine has an SGW lower, forged way back in 1983.

When Pmags first came out, they were all the rage. I got one, it was tight as hell in that lower. Made me hate 'em.

Years later, I run gen 2 Pmags in that lower, they drop free just fine. Glad they redesigned them. They’re all I buy now.

10

a buddy recently had this same problem with an Anderson. he plans to return it. if that doesn’t work, i guess we can always take down the anodizing…

11

Thanks for the replies. I’ve reached back out to aero, but have received no response.

I’m glad this is not a very expensive item. At this point I’ll file it, use it as a beater, and just move on.

Is there a quick and easy way to identify where I need to start filing? Maybe spray painting a mag and seeing where the paint rubs off?

12

You can take a mag, and a sharpie, and “paint it up”, insert and remove it a few times, it’ll show you the tight spots, like machinists dye.

I just put a mag in the stripped lower, and shined a bright light, here and there, different angles, in the magwell with the mag in, and saw where it seemed tight.

Go slow, file, sand, check fit, repeat.

13

Make sure the mag catch isn’t adjusted too tight.

14

Sounds like a plan. Thanks for the tip.

15

Take the magazine catch assembly off your lower so you can freely move a magazine back and forth through the mag well. Apply some sticky back fine grit sandpaper to the a magazine and slide back and forth, using the magazine as a sanding block until it’s as loose as is acceptable to you. Than spray paint the inside of the mag well where the wall was sanded down if you so desire.

My thoughts…

16

I’ve had mags fit tight in magwells because the mag release was adjusted incorrectly. Simply loosening up the mag catch solved the problem.

17

This. I had some fitment issues with my USGI mags in my Aero M4E1, I rotated my mag catch out one revolution and now everything drops free and inserts as I would expect.

18

I experienced the same thing from an Aero gen2 lower a couple of years ago. Gen 3 Pmags are so so and usgi mags were 0/50. As in not even close to making it to halfway seated. Live and learn.
Same experience with zero response from Aero.

S/F
Ryan

19

Good advice, but this magwell is tight without the catch installed.

20

After several issues with tight magwells over the years, I take a set of calipers with me and inspect it prior to accepting it. If it measures less than .900" at the front and back of the magwell, I will reject it.