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Thread: Buffer tube/buffer retainer question

  1. #1
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    Buffer tube/buffer retainer question

    Hey guys,

    Well last night I assembled my very first AR lower and I am very pleased with how everything fit together. I had to be a bit patient waiting for parts to come in and I kinda went with all upgraded parts for my first. Installing the detent for the front take down pin was surprisingly easy despite everything I read on the net. The hardest part was probably pushing the hammer pin though as I was thumbing the hammer into place against a lot of spring pressure.

    The question I have is related to my buffer tube/buffer retainer.

    I am running a BCM mil-spec tube with an H-buffer and an RRA LPK.

    While screwing the tube into the receiver, it comes short about 1/8th of a full revolution before hitting the nipple of the buffer retainer. When I backed it out a full turn, I noticed that it barely captures the retainer. With the stock fully collapsed, there is also an annoying small gap between the castle nut and the front of the stock. The end of the tube is also noticeably recessed into the back of the receiver. Here are some pics:





    I removed the buffer retainer and reinstalled the tube and everything and made that last 1/8th of a turn just to see how everything would fit. The end of the tube comes exactly flush with the edge of the top of the lower and the stock closes quite nicely with just a hair of extra space.

    Basically everything looks like it would fit a lot nicer if I managed to get that extra full turn.

    It doesn't look like the tube is protruding too much from the centerline of the buffer retainer nipple. Maybe like a 64th of an inch. I am thinking bout filing a small notch or just filing down the extra portion of the tube (coming out only at the base of the tube area) hitting the nipple.

    What would you guys do? leave it? do it? I heard only commercial tubes have that notch and i'm the kind of person who always wants to keep everything "standard" but i'm guessing my lower/parts are somewhat out of spec here and there which is amounting to this issue. I just wanna make sure I don't screw anything up as I've put quite a lot of money into this lower already. Is there anything wrong with having the front of the tube resting exactly flush against the edge of the lower? or is it supposed to be recessed into the threaded portion a little bit?


    Thanks!
    Last edited by Brandon04GT; 01-04-13 at 20:50.

  2. #2
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    What lower do you have?

  3. #3
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    Quote Originally Posted by shaneinhisroom View Post
    What lower do you have?
    It's a JD Machine lower....which seems to be plummeting in the quality control department lately...

  4. #4
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    Don't OCD about the gap between the stock while fully collapsed.
    That is totally irrelevant.

    Your end plate looks backwards in the picture. The raised knob should go into the hole in the rear of the receiver.

    Check how an upper fits. It may not fully close with the tube screwed in an extra turn.

    If the buffer retainer is secured without the extra turn, leave it there.

    After everything is verified and function tested, stake the end plate into the castle nut with an auto spring punch.

    ETA:
    http://m4carbine.net/showthread.php?t=91530
    Last edited by Clint; 01-04-13 at 21:08.
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  5. #5
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    I have seen DPMS tubes that have a notch in the tube. Is there enough thread on the top of the receiver so it does not protrude and interfere with the upper if you do notch?

  6. #6
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    I had the same issue with one of my builds. when the tube is screwed in the full length, it wound bind the retainer pin and if unscrewed one turn would barely catch the retainer by the edge. I just took a file and removed a little from the lip to keep the retainer pin from binding and the tube is screwed in flush with the lower with no stock gap.

  7. #7
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    Looks ok to me. You're GTG, so long as it doesn't pop out.
    As Clint suggested, function test. Also, try working the retainer several times to see if it has any semblance of popping out.
    Secondly, are you running a QD endplate? If it's a standard one then it's definitely on backwards.

    It's a JD Machine lower....which seems to be plummeting in the quality control department lately...
    How many JD Machine lowers have you worked on or know of, firsthand, that have had spec or QC issues?

  8. #8
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    I would fit the parts

    Since you know that the retainer is barely being held, why not fit the tube to the lower and make it all right.

    The end plate is shown in an incorrect position, as noted in above post.

  9. #9
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    Thank you everyone for the replies. The end plate is actually on correctly...it's a Noveske QD one.

    I don't actually have an upper yet, this will be my first ever AR. Unfortunately, it looks like i'll be hard pressed to find anything AR for the next coming weeks and months.

    After looking at things closely again, the buffer tube is so close to clearing the nipple on the retainer that I think I will needed just touch it with a few strokes of a needle file and that should work fine.

    I took a pic of how it will look with an extra full revolution of the buffer tube. Based on everyones' experience, would you say that the buffer tube would get in the way of the upper?




    Thanks

  10. #10
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    Quote Originally Posted by Col_Crocs View Post
    How many JD Machine lowers have you worked on or know of, firsthand, that have had spec or QC issues?
    Just briefly: I purchased two a few months ago without fully inspecting them. I noticed that both of them had lots of small blems here and there that seem consistant with what I would see on discounted "blemmed" lowers. I contacted JD who was very pleasant to deal with and they basically arranged for my to exchange them for a new pair and I would pick them up at a gun show a month later.

    When that time came, I picked up my new pair without pulling them out of the foam sleeves to inspect them. I was told they were personally inspected and GTG. Both of them still seemed to have a few small things here and there but not a big deal at all. Except, one of them had this:



    Not sure how this passes their QC.

    Now this is not first hand, but I've heard of other people hearing of similar issues popping up lately too.

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