Some time ago I picked up an AERO M5 (.308 size) lower at a gun show. A couple weeks later I purchased an completed (with forward assist and dust cover) directly from AERO. More recently I purchased a lower parts kit from AERO and yesterday I locked the lower and upper together using the pins in the parts kit.

To my surprise, there was a rather large gap between the two parts. I contacted AERO and they agreed that while the parts were functional the gap was excessive.

AERO is sending me UPS labels to send the parts back for replacement with parts that fit properly.

I love companies that stand behind their products - kudos to AERO.

oops!
great they took care of it for you.

Thanks for sharing. Good to know who stands behind their work!

Wow not bad for someone just being anal about a cosmetic issue.

That's great. I've had good response from their folks so far. My upper/lower, both ordered from them within a few weeks of each other, fit at least as good as yours. The lower is a blem, but I can't tell why.

Only issue I ran into was that I needed to file, ever-so-slightly, the rear pin lug on the upper. The fit was so tight that it would completely close. I used a standard file, and carefully made equal number of passes on each side until the fit was snug, but workable. She's tight with no wiggle, even without the adjustment screw being used.

Some folks get it, that if you buy two seperate parts at two times, that tolerances can stack and thats life.

Others make it work out.

Still others should have bought a matched/mated set all at the same time.

And then there are a few that realize, that gap has NO relationship to anything functional or accuracy wise, except in your head.

Having trained and worked as a machinist using CNC equipment, I understand stacked tolerances. I also understand that with proper care even cheap CNC machines are capable of far greater precision that these parts exhibited. I don't know what equipment AERO uses but they claim that "By personally designing and engineering state of the science tooling in-shop, we’re able to leverage the latest machine tool technologies to provide you with components of the highest quality". They also claim to maintain "razor thin tolerance levels".

Modern machining centers can maintain +/- .0002" positioning accuracy with .00008" repeatability. Some centers are even better, some worse. The days of +/- .001" tolerances are long gone for "state of the science" equipment. Even at +/- .001", though, it takes a LOT of stacking or poor design prints or tooling/equipment maintenance to get to a .0275" gap.

The reason I purchased an AERO upper was the expectation of higher quality and tighter tolerances, as claimed, and that the two AERO parts would mate properly. After viewing the same photo I posted here, AERO agreed the gap was, to use their word, "excessive".

I agree the problem is mostly cosmetic, although the gap is large enough to allow foreign matter to get into the rifle's inner workings. Cosmetics, however, are not unimportant to me as an end consumer purchasing non-blem parts. If you bought a new car and the paint started peeling off before you got home, would you just shrug your shoulders and accept it or would you head back to the dealer?

Bear in mind that I did not ask AERO to replace any parts but rather just asked them to review the photo and tell me if the gap was normal.

Could I have lived with the gap? Sure, but when AERO admits it is "excessive" by their standards and wants to make it right, what is wrong with allowing them to do so?

While the gap was excessive, "allowing foreign matter to get into the inner workings" is a non issue. Think hole for trigger, magazine clearance etc...

I have an Aero upper and am so totally unimpressed with the claim "By personally designing and engineering state of the science tooling in-shop, we’re able to leverage the latest machine tool technologies to provide you with components of the highest quality". They also claim to maintain "razor thin tolerance levels".

But it works and every company out there has a sales pitch.

You may consider it a non-issue. I do not.

One of the big complaints about AR-style rifles, and particularly those designed for .308W size cartridges, is their weight. If dirt/dust/rain/ice/etc. were not issues, why not lighten the thing up by drilling holes in it until it looks like Swiss cheese?

Not surprisingly, I don't see any manufacturers of any long arms doing that to their receivers or uppers.

That said, I do not consider it a big issue. My Rock River and S&W AR rifles show similar gaps -- but they are much, much smaller.

After viewing the photo AERO stated the gap was excessive and did not meet their standards. Had AERO said the parts were within spec that would have been the end of it but instead AERO offered the replacement.

So back to my original point, kudos to AERO for standing behind their product.

I'm with you it would not have worked for me either I like mine tight. I have a lot of Aero Precision products and they build nice stuff and do have good service.

Not quite Swiss cheese

http://www.thefirearmblog.com/blog/2014/02/20/aero-precisions-skeletonized-ar/

I found this kind of amusing..
https://www.youtube.com/watch?v=LQalucXr_tQ