9MM AR Pistol Build Issue

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  • IX-3

    Active Member
    Aug 21, 2018
    424
    Eastern Shore, MD
    Hopefully this is the right forum, I wasn't sure if it should go under Gunsmithing or Rifles.

    I'm in the process of building a 9MM AR and have hit a problem. The upper and lowers are together but I'm having a problem with them not fitting together properly.

    Lower Build:

    KE Arms 9MM Glock Lower
    Aero LPK
    Aero Enhanced Pistol Buffer Kit
    Geissele Maritime Bolt Catch

    Upper Build:

    Aero Assembled Upper
    Aero Atlas S-One Handguard
    Faxon 9MM 10.5" Barrel
    VG6 Gamma 9MM
    Brownells Branded 9MM BCG (Faxon)
    Radian Raptor LT Charging Handle


    Here are all of the scenarios I tried.

    1) Placed upper on lower and inserted rear takedown pin. Front pivot pin would not go in.

    2) Pivoted upper and inserted pivot pin. Rear of upper would not mate to lower.

    3) Removed BCG and charging handle, inserted pivot pin. The upper mated to the lower fine and the rear takedown pin was able to be inserted completely.

    4) Reinserted charging handle, repeated #3. Same result as #3.

    5) Removed buffer and spring, reinstalled BCG. Same results as #2. Rear of upper would not mate to lower.

    6) Removed Raptor and installed standard Mil-Spec charging handle. Same Result as #2. Rear of upper would not mate to lower.


    The BCG is sitting flush with the rear of the upper receiver.

    The first photo is with the BCG installed, the second is with it removed, and the third is a full view with the BCG removed.
     

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    alucard0822

    For great Justice
    Oct 29, 2007
    17,643
    PA
    check the ejector, sometimes there is a clearance issue between that and the underside if the bolt. Pretty much a given you will have to tweak the ejector and LRBHO to get them to work, or get sufficient clearance.
     

    IX-3

    Active Member
    Aug 21, 2018
    424
    Eastern Shore, MD
    check the ejector, sometimes there is a clearance issue between that and the underside if the bolt. Pretty much a given you will have to tweak the ejector and LRBHO to get them to work, or get sufficient clearance.

    Will do. The lower doesn’t have LRBHO so at least there’s one thing that won’t need to be tweaked.
     

    rseymorejr

    Ultimate Member
    MDS Supporter
    Feb 28, 2011
    26,015
    Harford County
    I ran into that problem with my AR10 build. I have an Aero Precision stripped lower, the complete upper was NOT Aero Precision. I ended up buying a srtipped Aero Precision upper receiver and swapping everything over. My AR15's have never been a problem.
     

    ToolAA

    Ultimate Member
    MDS Supporter
    Jun 17, 2016
    10,500
    God's Country
    Which trigger are you using? I have this issue on my 300BO with the Echo trigger. The way I solve it is to attach the upper about 1/16” fwd of the takedown pin alignment position. Then push the upper back until the holes align then insert the takedown pins.


    Sent from my iPad using Tapatalk
     

    IX-3

    Active Member
    Aug 21, 2018
    424
    Eastern Shore, MD
    Which trigger are you using? I have this issue on my 300BO with the Echo trigger. The way I solve it is to attach the upper about 1/16” fwd of the takedown pin alignment position. Then push the upper back until the holes align then insert the takedown pins.


    Sent from my iPad using Tapatalk

    I'm using the stock trigger from the Aero LPK.
     

    IX-3

    Active Member
    Aug 21, 2018
    424
    Eastern Shore, MD
    Update: I tried ToolAA’s suggestion with no luck. I also tried the bolt in my brothers AR that has both an Aero upper and lower. The bolt went in fine and he was able to mate the two with zero effort and install the takedown pin. I’m going to look into the ejector tomorrow.
     

    Rab1515

    Ultimate Member
    Patriot Picket
    Apr 29, 2014
    2,081
    Calvert
    95% chance it is an issue with the ejector, most of the time they need to be tuned anyway to get them as close to the firing pin as possible.
     

    alucard0822

    For great Justice
    Oct 29, 2007
    17,643
    PA
    most of the time, the ejector rests in a channel cut into the underside of the bolt, if the ejector has sharp edges, or doesn't line up exactly, it will hit. Can usually tell by locking the pivot pin in, pressing tape into the bottom of the bolt following the countours, then closing the upper, and seeing where the tape is rubbed, marking paint works better, if you have it. Most need a little deburring or bending one way or the other. sometimes you get the best function with the ejector "nose" bent slightly inward twards the firing pin if there is too much slop.
     

    Rab1515

    Ultimate Member
    Patriot Picket
    Apr 29, 2014
    2,081
    Calvert
    most of the time, the ejector rests in a channel cut into the underside of the bolt, if the ejector has sharp edges, or doesn't line up exactly, it will hit. Can usually tell by locking the pivot pin in, pressing tape into the bottom of the bolt following the countours, then closing the upper, and seeing where the tape is rubbed, marking paint works better, if you have it. Most need a little deburring or bending one way or the other. sometimes you get the best function with the ejector "nose" bent slightly inward twards the firing pin if there is too much slop.

    Lip Stick on the ejector works well as well. Just make sure you use one that your wife/girlfriend wont mind loosing :innocent0
     

    IX-3

    Active Member
    Aug 21, 2018
    424
    Eastern Shore, MD
    Ok so I loosened the set screws on the ejector and then adjusted it slightly this morning. Now the upper and lower mate together perfectly with the bolt installed. However, the bolt seems to be scraping the ejector and felt stiff when pulling it back until it was past the ejector. I've attached a couple of photos of the ejector afterwards.

    I'm also pretty sure my Maritime Bolt Catch is not going to work on this lower due to the shape of it. I couldn't get it to actually catch the bolt. I think it's because the MBC is so big it's hitting the lower before it can move enough to catch the bolt. I'm going to throw the bolt in my brothers AR again and see if it will catch since he also has a MBC installed.
     

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    MindTheGAP

    Active Member
    Jan 4, 2018
    574
    Maryland
    I've never see that much in the way of issues with the ejector, but I know that certain bolts aren't cut properly even when they're bespoke '9mm' bolts. I've had a buddy's rifle look like that and he ended up polishing the underside of the bolt and taking down the ejector a bit.
     

    Rab1515

    Ultimate Member
    Patriot Picket
    Apr 29, 2014
    2,081
    Calvert
    Ok so I loosened the set screws on the ejector and then adjusted it slightly this morning. Now the upper and lower mate together perfectly with the bolt installed. However, the bolt seems to be scraping the ejector and felt stiff when pulling it back until it was past the ejector. I've attached a couple of photos of the ejector afterwards.

    I'm also pretty sure my Maritime Bolt Catch is not going to work on this lower due to the shape of it. I couldn't get it to actually catch the bolt. I think it's because the MBC is so big it's hitting the lower before it can move enough to catch the bolt. I'm going to throw the bolt in my brothers AR again and see if it will catch since he also has a MBC installed.

    Use pliers to gently adjust where the ejector sits in the slot. You want to pull the bolt back to where the ejector and bolt face are flush and look at where the gap in the bolt slot is. Bend the ejector as close to center line of the bore as possible without rubbing, permanent marker works well to test for rubbing. Not all bolts/uppers/lowers have the slot/ejector in the same place and should be adjusted for fit, we are talking sub millimeters here.
     

    IX-3

    Active Member
    Aug 21, 2018
    424
    Eastern Shore, MD
    Ok update. After everyone suggested the ejector was the problem I went looking online for some YouTube videos since I wasn't home so that I had some ideas to try when I did get home. While doing that I found a post on the AR15 forums about a guy having the same issue but with a PSA dedicated lower. He solved it by shimming the extractor with a .001 thick piece of brass. So after finding a small sheet of brass on Amazon for $8.85 and paying the $3.99 upgrade fee for one day shipping the brass arrived this afternoon. I trimmed a piece to fit between the ejector and lower without protruding from the ejector slot. I put the upper back on and the bolt now slides back and forth without hitting the ejector.

    I also had two Glock magazines and a Magpul magazine show up today so I can actually shoot it until I get up to Cabela's in Wilmington. So if all goes to plan I should be able to take it to the range Thursday and try it out.

    The only thing left to do is replace the bolt catch because the Giessele Maritime Bolt Catch does not function with the KE Arms lower (it can't move far enough due to the shape). Then I just have to install the MBUS sights and my Vortex SPARC II.

    Thank you all for the help, it's greatly appreciated.
     

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