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AR guys: NFA poly lower help? Can't install mag catch

Discussion in 'Rifle Country' started by 1KPerDay, Mar 25, 2013.

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  1. 1KPerDay

    1KPerDay Member

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    Update as requested: got the mag catch fitted... it's still a little funky depending on how you press the button. But using the first finger in the usual way it works fine. Pressing more from the front will sometimes move the opposite side (the latch) into the wall of the opening and it will stick a bit, but it still works either way. The rearward curve of the opening needed the most work. Got the bolt stop in, with just a little filing of the inside edges of the notch. Pmags fit fine and drop free; an Adventure Line USGI fits and locks but is a bit snug. I find that a bit weird. I don't really want to file the magwell so I guess I may just use Pmags in this rifle (or fit it for .22 conversion mags...).

    Got the trigger group in (I'm using a PSA LPK); the holes for the pins were quite a bit too small (quite a bit meaning I needed to sand them a tad larger before I could drive the pins through). I left them pretty snug as I figure tighter is better than loose; you still need a punch to drive them in and out. At first I thought the disconnector wasn't going to work properly (with trigger held back, I couldn't press the hammer back to the disconnector hook without releasing the trigger pressure slightly; but once safety was fitted and installed, the trigger/disconnector feel and work fine. Dunno if that's normal for ARs; this is my first "build".

    The holes for the safety were very tight; I sanded them until the safety rotates with a little thumb pressure (without the detent installed). I would keep going until it flops about under gravity but I imagine it will wear in a bit and I don't want it to get too loose.

    The front takedown pin is snug, and I left it that way. You have to drive it out of the left side hole (it slides freely after that). Rear takedown pin fits a bit better but still a bit snug. I figure that's okay.

    Overall the only real difficult bit so far was the mag catch.

    The notches to allow the upper (where the takedown pins go through) are very snug; particularly the rear one. I can get my PSA upper onto the lower (haven't tried with pins yet) but I have to knock/pry it off out of the rear slot. I filed a bit of flash off, but it still may need more. I imagine tighter is better than floppy/loose so I don't want to overdo it with making space for the upper. I'll try a couple other uppers and see if it's too tight across the board, and then remove a small amount.

    I'll post an update and maybe a video when I get it finished to my satisfaction, and a live-fire test. Anyone got a lightweight barrel for sale?:)
     
  2. 1KPerDay

    1KPerDay Member

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    One more major problem: the threads for the grip screw seem to be either the wrong thread pitch (unlikely) or the entrance to the hole is buggered so the threads of the screw don't enter properly (likely). I messed with it for an hour and finally, in frustration installed the screw and grip using overmuch elbow grease. I'm sure it's cross-threaded and messed up now. But it's tight. If I ever have to remove the grip I'll have to tap it for a larger screw I guess, or maybe install a metal insert.

    The Magpul MOE grip I intended to install would not fit; the tab on the receiver was at least 1/16" too thick. The ERGO and USGI grips I tried fit fine, though the ergo's safety detent spring hole wasn't deep enough and the spring prevented full seating of the grip. I installed the USGI type grip.

    That and the magazine catch are the major problems... fitting the bolt catch, trigger group pins, and safety are minor issues.

    Video discussion here for any interested
    https://www.youtube.com/watch?v=HsCbm4ANry4
     
  3. taliv

    taliv Moderator

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    good grief. i know the feeling though. i had a lower that i paid $$$ to get painted and then found out it was out of spec and it took a while to get it working. very, very frustrating
     
  4. 1KPerDay

    1KPerDay Member

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    Yeah, this was pretty much out of curiosity and for my education. I wouldn't do it again, and I won't use the rifle for "serious" purposes.

    If it turns out that it actually works and is reasonably durable, It'll be worth it.

    One thing I can't believe is that they expect a steel bolt to reliably hold in plastic threads. That's just plain ignernt. :rolleyes:
     
  5. justice06rr

    justice06rr Member

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    Well, you live and learn. Good to hear you got it assembled anyway.

    Buy an aluminum lower for your next build and you will see how easy it is for parts to be installed. PSA seems to be getting stripped lowers regularly now for $120, and I also saw the LPK in stock for $60.

    Good luck with the rest of your build.
     
  6. 1KPerDay

    1KPerDay Member

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    That's good to hear. :cool:

    I completed the initial live-fire evaluation this morning and it functioned perfectly with both .22 and 5.56 uppers. Trigger feels quite good (it is a PSA LPK as noted above), bolt locks open properly, no malfunctions, no issues. One upper was a bit more snug in the rear pin hole but it installed and removed fine. That one also had a bit tighter tolerances on the top of the receiver near the charging handle, and the first couple of times I opereated the bolt one handed it seemed to rub a bit, but after a couple of times I guess the extra poly wore down and it worked fine.

    I can't really feel a significant difference in weight between an aluminum lower with receiver extension/buffer tube, spring, and buffer installed, and the poly lower with the same. I need to get a postal scale. But I imagine a poly lower with a poly LPK would save a bit of weight.

    So far, I'm liking it quite a bit. The other USGI mags I tried fit fine and drop free, as well as the CMMG .22 mags.

    I'll post a video update soon for those interested.
     
  7. 1KPerDay

    1KPerDay Member

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    http://www.youtube.com/watch?v=4F7BOdrYasM

    Works fine! Started with .22 conversion in case something was obviously wrong; no issues. .223 upper worked perfectly as well. Yay! Hopefully it proves reasonably durable.
     
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