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essjay
12-20-2016, 8:46 PM
Built-up a Gen 2 Aero Precision lower recently to supplant my Gen 1 AP lower. Put the old upper (Aero Precision M4E1 with a Seekins rail) on the new one to check the fit, and noticed that the rear takedown was extremely tight to remove, but otherwise seemed fine.

So, my new upper shows up today, normal Aero upper with an ALG V2 rail on it. I try to put it on the new lower and... the front takedown won't go in. I then put the new upper on the old lower and and it fits perfectly fine. So, then I attach the old upper to the new lower and find that it fits, but like before, the rear takedown is super tight.

So I try the new upper again, and while I can get the rear takedown in and out fine, the front just won't slide in. So I try the rear hole of the upper in the front takedown slot, and it slides in fine. Then I try the front hole of the upper in the front takedown slot, with the upper vertical and reversed, and it slides in fine.

Trying again, I fail to get the front takedown to go in, so I slide in the rear takedown to lock it in place, look at it real close, and notice that the ALG handguard is in contact with the front right takedown ear of the new lower. I put on the old upper and find the same situation is true, but I can still attach the upper because the rail is just slightly further away from the upper at that point.

Looking at the new lower, it seems to me that the right ear is just slightly larger than that of the left (or the old lower). So, given that I can't just call up Aero and ask them to replace the slightly out-of-spec lower with a good one due to the fact that it's December 20, 2016, should I just file the ear down and hope for the best?

edit: I have a terrible camera, so I've drawn it out a bit here using some stock photos.

http://i.imgur.com/ww1ioLh.jpg

Kwikvette
12-20-2016, 8:47 PM
Pictures will describe more than your 4 paragraphs.

essjay
12-20-2016, 8:49 PM
I have a terrible camera, so I'll try some Photoshop.

Kwikvette
12-20-2016, 8:52 PM
Lol

Camera phone? Just make sure you've got some lighting.

FMJBT
12-20-2016, 9:04 PM
I'd file on the handguard rather than the lower if possible. Pics would definitely help.

damon1272
12-20-2016, 9:08 PM
BFH and a drill will do you!

electric7
12-20-2016, 9:18 PM
Lube it up, should loosen up with time. Its better they are tight than loose I think. File it down if needed.

essjay
12-20-2016, 9:23 PM
Lube it up, should loosen up with time. Its better they are tight than loose I think.

It's not a lube thing. The handguards on both uppers are in contact with the takedown ear of the lower. One the old upper, it's forcing the upper to the rear slightly and causing the rear takedown lockup to be tight. On the new upper, it's simply not allowing me to line up the takedown holes on the upper with those on the lower.

manuelcardenas77
12-20-2016, 9:27 PM
I'd file down the upper, I wouldn't touch the lower. My 2cents

CoopsDad
12-21-2016, 5:51 AM
I'll repeat what others have said- file on the replaceable part, the handguard, rather than the hard to replace lower.

essjay
12-21-2016, 6:30 AM
The ironic thing here is that I got the new Aero lower instead of paying less for an Anderson lower after the LGS employee told me that he'd had a few complaints from customers about fitment issues with the Andersons; I distinctly remember telling him that the fit on my prior Aero build was great. Oh, well.

essjay
12-24-2016, 9:33 AM
Tried a friend's upper, had the same problem, and ended up filing about half of a millimeter off the inside edge of the right ear with a medium-coarse bastard file. Going to want to refinish it at some point, but at least it won't interfere with installing and hinging uppers anymore.

CouchOperator
12-24-2016, 10:02 AM
File the upper/handguard.