First Time AR Builder...Help Needed

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  • E7Wrangler

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    Apr 21, 2016
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    Got my feet wet putting together an AR lower for the first time, great fun with my son. Found some great instruction videos on youtube and got ALMOST everything together. Big question, the upper (already built kit from PSA) and lower won't go together. The lower is an Anderson Mfg receiver bought locally and a PSA parts kit. I can snap in either the front pivot pin or the back pivot pin but not both when trying to join the upper and lower. With the front pivot pin snapped in and feeling in the rear pin holes with a toothpick I can feel that the three holes are not fully lined up, there is a ridge from the upper sticking up slightly out of alignment.

    I put the completed upper on a different lower from my current rifle and it fit fine. The upper from my current rifle fit fine on the newly built lower. What gives and how do I get this fixed?

    I have basic hand tools but no gunsmith tools or machining tools or experience. I am fairly competent with tools and building but certainly not trained or a craftsman. I am not afraid or to proud to get help. I Live in Lebanon, IN so looking for easy suggestions to fix on my own or recommendations of where to take the gun for fitting. This is a budget starter gun for my son to shoot and participate in shooting sports with, high dollar improvements and customization are not in the cards. Thanks in advance for your help.

    Yes, you can make fun of me, I can take it.
     

    cmann250

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    Pictures help. Does the rear take down pin fit through the rear take down lug when the rear take down pin isn’t installed in the lower? Might be an alignment problem


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    1911ly

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    It sounds like a defect in machining. Can you post a pic of the lower top and side view? If you have a dial caliper (?) Measure the distance between the pin holes and there heights. Look for rubbing marks on the lower casting. There might be a tight fit some where.

    And if you haven't tried it yet, remove the bolt from the upper and see if it will let you put the pins in. FCG holes could be off? It could be anything. Compare everything you can.
     

    Wolfhound

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    Maybe I am looking at this all wrong but why not use his lower with your upper and your lower with his upper. Two working rifles with no repair or tweaking needed problem solved. :scratch:
     

    E7Wrangler

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    Pictures help. Does the rear take down pin fit through the rear take down lug when the rear take down pin isn’t installed in the lower? Might be an alignment problem

    Yes, the rear take down pin does fit through the rear take down lug and the holes on the lower if I don't have the front take down pin in. It's only when I try to get both take down pins engaged that the problem arises.
     

    E7Wrangler

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    It sounds like a defect in machining. Can you post a pic of the lower top and side view? If you have a dial caliper (?) Measure the distance between the pin holes and there heights. Look for rubbing marks on the lower casting. There might be a tight fit some where.

    And if you haven't tried it yet, remove the bolt from the upper and see if it will let you put the pins in. FCG holes could be off? It could be anything. Compare everything you can.

    Pictures should be attached (if I did it right).

    I don't have a dial caliper.

    I don't see any rubbing marks.

    I did try removing the bolt and putting the upper and lower together, no change, didn't fit.

    If it is a machining defect why would both the upper and lower mate just fine with the upper and lower from the other rifle?

    I appreciate the help.
     

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    cmann250

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    Sounds to me as though one set of take down holes is positioned out of spec.

    If the upper fits on a different lower, logic says there’s something wrong with the lower.


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    E7Wrangler

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    Maybe I am looking at this all wrong but why not use his lower with your upper and your lower with his upper. Two working rifles with no repair or tweaking needed problem solved. :scratch:

    Certainly a solution. I would rather not as my rifle is a level or two better than the new one for my son. Also it ticks me off that the new one isn't going together as it should.
     

    E7Wrangler

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    [QUOTESounds to me as though one set of take down holes is positioned out of spec.

    If the upper fits on a different lower, logic says there’s something wrong with the lower.][/QUOTE]

    Yes, but my other upper fits on the suspected bad lower. Don't mean that to sound snotty, I just don't know much. I appreciate the help and replies.
     

    patience0830

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    Not far from the tree
    Stacking tolerances.. doesn't take much out of spec to put 2 round holes out of alignment with each other. Upper is a tiny bit far apart. Lower is a tiny bit too close. Not too much if mated to an upper thats in spec, but in combination, it just won't fit.
    Tinker toys for adults, yes. But tolerances count. Sometimes it pays to buy a prefit set.
     
    Last edited:

    rvb

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    remove trigger/hammer from lower and bolt from upper. make sure it's the location of two takedown pins interfering, not something else. if the rear pin goes in by itself and the front by itself, then that's probably the issue.

    next if it is the location of the takedown pins, grease the pins and see if some light tapping from a plastic or rubber mallet will get them in place. I've had several I couldn't hand push until I had worked them in/out several times. If there is actual interference, see which one is the culprit... easiest way is to pin one at a time and see which one aligns the little magwell "rib" on the left side of the lower with the matching decorative "bump" on the upper. hopefully not off more than a few thousandths.
    get some sand cloth from brownells, 200/400 grit should do. wrap it around something like a screwdriver or punch and take off a little material on the inside of the upper's hole. just on the side interfering. hit with some alumablack if you wish and done.

    if it's off more than a little, say there is a 0.1" difference, I'd be looking for an exchange/refund...

    -rvb
     
    Last edited:

    rvb

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    Yes, but my other upper fits on the suspected bad lower. Don't mean that to sound snotty, I just don't know much. I appreciate the help and replies.

    if that's the case, this upper works on different lower, and this lower with a different lower, I'd bet the grease + rubber mallet will work for you. Might have to tap it in/out a few times till it wears in. a light polish on the inside of one of the upper holes with some sand cloth will help, or use something like jb compound...
     

    Tactically Fat

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    I'd bet the grease + rubber mallet will work for you. Might have to tap it in/out a few times till it wears in.

    More than one time in my dealings with firearms some percussive therapy was all that was needed.

    Be judicious and precise with it.
     

    87iroc

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    My new rifle I built a few years ago was a 'bit grainy' trying to put the pins in. Light tapping, I think, and lubrication. If you can't physically see a mismatch. I'd say that's it.
     

    roscott

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    Sounds like tolerance stacking. Patience described it best.

    If they are not too far apart, you can likely drive the pin in, but you’ll have to drive it back out as well. I had a cheap PSA upper that was the same way. It only fit in certain lowers, but it worked fine in any of them after a bit of “persuasion.”
     
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