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.
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