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Thread: Aero Precision 308 Pistol BCG not locking back on empty mag

  1. #1
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    Aero Precision 308 Pistol BCG not locking back on empty mag

    I just built a Aero Precision M5 pistol. Everything is Aero Precision except for the SLR adjustable gas block, SBA3 brace, and AR15 JP Silent Captured Spring. Iíve put about 150 rounds through it and every time the BCG will not lock back. Even just putting an empty mag in it will lock back but any little movement will cause it to go back into battery. Iíve tried all the different JP springs, I tried switching the buffer combo to an Aero Precision M5 Pistol buffer kit and it will still not lock back. Any thoughts? Thanks for the help.

  2. #2
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    Does that include an Aero barrel? Barrel length? carbine length gas system? Aero lower parts kit?

  3. #3
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    Aero Precision 308 Pistol BCG not locking back on empty mag

    Doses the bolt catch function without a magazine or any movement and the bolt moves?

    Sent from my iPhone using Tapatalk
    Last edited by zombiescometh; 11-16-19 at 01:37.
    "The most important rule in a gunfight is: Always win and cheat if necessary." ~ Clint Smith

  4. #4
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    Yup 12.5 inch Aero barrel, carbine length gas system with Aero gas tube, and Aero lower parts kit. Bolt catch works good without the magazine. You can shake the gun and the bolt wonít move. Iím using PMags. I have a Sig 716 and they work perfectly in that gun. So I donít think itís the mags unless Aero has a history of not liking PMags but I havenít read that. I think Iím gonna order some different mags. See if that corrects the problem.

    There is also some ďwearĒ on the JP buffer. It looks like from just opening and closing the receiver because it is only present on half of the buffer head. The BCG is an Aero Nickel Boron. I would add a picture but I think you need one of those photo accounts.

  5. #5
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    You said you played with different buffer springs, have you played with the gas adjustments on the block? Like opened it up all the way, ensuring that it locks back, and then started turning it down?
    Sic semper tyrannis.

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    I should of mentioned that. I did turn the gas block down all the way to were it would not cycle. I then turned it up to were it would cycle. I then continued to turn it up and recoil became harsher. The gun will cycle and eject the rounds reliably. No problems there. Itís coming about at the 12 oíclock to 1 oíclock position now that I have it dialed in. Iíve shot about 150 rounds thinking it might need to broken in. Nothing has changed.

    Manually trying to get the bolt to stay locked back with an empty mag still does not work. It will stay briefly but any type of movement causes it to slam forward. Like I said before without a mag I can actuate the bolt catch and it will stay back even while moving and shaking the gun. I was hoping maybe there was an easy fix that people have had to deal with before.

    Going forward Iím gonna try some different mags and then maybe get a different bolt catch. Also put some rounds through and do some thorough inspections and lubrication. I appreciate all the help

  7. #7
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    With the upper removed, you can watch the follower of an empty magazine lift the bolt catch up as it's inserted. When the
    empty magazine is fully seated, pressing on the lower bolt catch surface will cause the bolt catch to rise above the position
    introduced by the follower by a small amount.

    If inserting an empty magazine and fully retracting the bolt carrier doesn't securely lock the carrier back, then the gas system
    isn't causing the problem, but it may still need to be adjusted beyond it's current setting.
    Last edited by grizzman; 11-16-19 at 13:42.

  8. #8
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    I will try that next time I go to the range. So with an empty mag in, I pull the charging handle back and the bolt will catch briefly and then slam forward.

    Without a magazine in, I pull the charging handle back and manually actuate the bolt catch to where itís 100% up and the bolt will stay put.

  9. #9
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    If the bolt catch will not catch unless you manually force it, that seems to be the problem that you should fix before tampering with the gas system, buffer, etc. Why isnít the magazine follower lifting the bolt catch sufficiently?


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  10. #10
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    Well Iím an Idiot and this is an example of why attention to detail is important. I was looking at my other AR and I noticed when it was locked back the bolt was a lot farther aft. Upon further investigation I realized the JP buffer was not allowing full travel of the BCG. The bolt catch was actually grabbing on the underside lip of the BCG.

    Now idk why I ordered this buffer after I had been doing research on this build. But after installing the correct buffer and spring it does lock back in the correct position with full travel.

    So for future reference an M5 will not work with an AR15 JP silent captured spring. Most people are probably aware of this but I donít spend much time on the forums. I know JP sells AR10 version. Not sure if that works. I need to do more research.

    Now I just need to get back to the range and do some more tuning with the gas block and the new buffer and spring. Thanks for the help and suggestions!

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