Aero precision lower issues

[pete57]

I'm having an issue with a bolt catch not consistently engaging with the magazine follower and depressing the follower allowing for the bolt to hold open on an empty magazine. The problem is intermittent. Sometimes the bolt catch engages the follower and sometimes it does not. The lower is aero precision. There are 3 possible culprits causing the issues.
1. Bolt catch is out of spec.
2. Magazine/follower is out of spec.
3. Aero precision lower is out of spec.

To eliminate the variables I isolated them.
First I tried different magazines, polymer and metal. Most magazines did depress the follower, but just barely engaged it. Others did not engage at all. The magazines were tried in a different lower and they worked correctly with no issues. Next I tried different bolt catches. I tried 3 different bolt catches. The results were the same, there was no improvement and the bolt catch still occasionally did not engage the follower. I tried two of the bolt catches in the other lower to see if they are the culprit, but all performed correctly with no issues.

So by swapping parts and magazines between two lowers I found that one lower, performed flawlessly with any combination of bolt catch/magazine. The other lower (aero precision), had failures with all combinations of bolt catch/magazine.

So I concluded the aero precision lower was slightly out of spec. After contacting aero precision they had me send the lower to them. They performed a quality control check, assembling the lower and said they found no issues. Currently the lower is in the mail back to me. I don't doubt they were able to assemble the lower and get the bolt catch to engage the follower. I was able to do the same thing. The problem is that it fails intermittently. It fails intermittently while other lowers, using the same magazines and bolt catches do not fail at all. I'm aware that it works most of the time. I didn't need to go through all this hassle for them to show me that it works most of the time. All machines have a certain amount of acceptable failure rate. If for example a handgun has one malfunction in 5000 rounds, that's a pretty acceptable failure rate. The failure rate of this lower is not acceptable to me. I'm disappointed it's acceptable to aero precision. Here are a couple pics of the issue.
2.jpg

3.jpg

[GH41]

What magazines? The plastic one pictured looks kinda crusty. Can you post a picture using a newer mil spec magazine? MagPul doesn't count.

[pete57]

I can't post pics now because I haven't received the lower back yet. Aero stated they tried gen 2 and gen 3 magpul when they tested it. I have tried many different magazines from various manufacturers all with similar results. All the magazines I tested were also tested in another lower and functioned properly....bolt catch engaging the follower with plenty of "meat". The magazine in the first picture is a gen 2 magpul. It's new, I don't think I've ever used it. The only solution I can think of is a bolt catch that is slightly longer where it grabs the follower. I don't think that exists though. Just trying to figure a way to keep this lower out of the parts bin when it comes back.

[AKDoug]

You can go here http://biggerhammer.net/ar15/cad/ar15_receiver.pdf for a dimensional plan of the AR-15 lower. You can do the math and measure your lower to see if it's in spec. From first glance it appears that the "tit" on the bolt catch protrudes into the mag well even with the "step" in the mag well. That is the same position my BCM and DD lowers place the bolt catch. I have three Aero lowers of early production that are also the same way.

What brand of magazines? What brand of lower parts kit?

[AKDoug]

Sorry we posted at the same time earlier. Copy the brands of mags.

Here is a pic of one of my AP lowers using a DD LPK and DSG arms aluminum mag. Batteries are dead in my micrometer or I’d give you some measurements.



Sent from my iPhone using Tapatalk

[pete57]

The magazine in the second picture is a palmetto state aluminum magazine. I can't remember the lower parts kit I used. I used an ALG defense trigger, shouldn't matter though. The bolt catches I tried were POF, Spikes, and I think a palmetto state one. Same results with all of them. I think the problem may be with measurement "B" in the pic below. If this is off slightly it would move the bolt catch too far from the magazine well.
1.jpg

[AKDoug]

Keep us posted on the results when your lower gets back.

Are those measurements calculated from the plans? The magwell dimensions on my D.D. lower jive with those, but the "B" distance on my lower is .1025" and the "c" measurement is .1640" This lower has the most bolt catch protrusion into the mag well of the lowers I have.

[Esq.]

Keep us posted on the results when your lower gets back.

Are those measurements calculated from the plans? The magwell dimensions on my D.D. lower jive with those, but the "B" distance on my lower is .1025" and the "c" measurement is .1640" This lower has the most bolt catch protrusion into the mag well of the lowers I have.

Had a similar issue with an Anderson lower I was building a pieces parts gun on. The pocket for the bolt catch was too narrow and the catch-and I tried several, would bind slightly.

When gunsmithing, I was always taught to modify the cheapest part....So, I took the bolt catch out to my belt grinder and gave it a little kiss....a touch of aluma black and good as new...1500 rounds later and not an issue, runs like a top.

So, not ideal, ideal being a perfect lower, but, a reasonable fix.

[Buncheong]

Been contemplating a Aero lower for a clone build I’d like to do.

The more I see/hear/read these detailed accounts of out-of-spec lowers, the more my clone idea using Aero goes in the round file.

[JohnXDm]

I have built 10 AR's, 9 of them using Aero Precision receivers. They're all made by CNC machines using the same computerized program with the same dimensions. Can't see how a few could be out of spec.

I have not had a single problem with any of mine.

https://www.aeroprecisionusa.com/manufacturing-and-oem