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Thread: Barrel and upper

  1. #1
    Gunco Rookie BushBack15's Avatar
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    Question Barrel and upper

    Hi everyone. New to being here . i'll jump into what I'm up against. I'm Building SP1 or what l call SP2 versain of AR. I have A1 upper no assist Used Heavey Barrel 1/7 twist. My Question is the Barrel Nut or Exstention where bolt locks up to barrel and Index pin is not centered to upper. It is off 1/8 of inch to left of Index noch in upper. has anyone had simular problem? Yes all parts are US military issue. Upper is brand new, barrel and exstention is Used but in very good shape . Bolt locks into it OK but haven't installed it Because, Index pin off the Gas tube and Sight are off. any Suggestions?

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    gunco irregular moleman's Avatar
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    Is the barrel extension original to the barrel and has it never been removed? I only ask as there have been quite a few used barrels sold lately without the barrel extension and it is very difficult to get another one to time correctly. Is there any side to side play with the pin in its slot in the receiver? If so shim it. If its the original barrel extension that came with the barrel and its never been removed then most likely your front sight base is canted and must be straightened. Take the front sight base off and make sure the gas port is in line with the barrel extension index pin. if it is, you have just confirmed the front sight base is canted. The easist way I can tell you to fix it is to drill the pins hole a little larger and install larger pins. To center it install the barrel in the receiver and the front sight base without its pins. place the barreled upper upside down on a flat surface like a kitchen counter top and try to rock it back and forth. It should rest evenly on all four sight ears when its on straight. Re drill the holes a little larger and you're good to go. I also have straightened a front sight on a FAL by peening the displaced metal back into position. You could always just put a clamp on style front sight base as well.

  3. #3
    Gunco Rookie BushBack15's Avatar
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    No the exstention is not orginal to barrel so I'm sure your correct in it not being in time. But everything lines up with just 18 turn. Could I cut new noch out in upper to line everything back up or world this be to far out. Even load ramps at bottom line up correctley. Thanks for all you've given. Just maybe I'll order another from Numrich to see if it will align better. I have brand new DPMS one but it is even farther off. thanks BackBush15

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    gunco irregular moleman's Avatar
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    No cutting the notch over to get the pin to center the front sights will make the bolt and barrel extension out of time and the bolt will hit it as it closes. Did it headspace ok? Your best bet at using that barrel without a lathe and a chamber reamer would be to find a barrel extension that you can hand tighten to the 10:30-11:00 position. Use a pencil to run a mark from the gas port back to where the barrel extension pin should be (this will be your 12 O'clock position) to help line it up. Make sure you check that headspace when you're all done.

  5. #5
    Gunco Rookie Pappy63's Avatar
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    First thing is get a Tech Manual (TM 9-1005-249-24&P) Or (TM-05538C-23&P/2) . You can find thease on line as a free download. Read the manual there are several sections on Front sight/ rebarreling problems . Read and understand what you are doing.
    One thing you may want to check is with the front sight removed and the barrel nut and reciver mated to gether, is the gas port aligned along the same plane as the in the notch of the barrel pin notch . ( Front sight pins get drifted out from the left side of the sight driving them to the right side from the chamber end) If so place the bolt in and test in the upper and see if the bolt willl lock to the barrel extension.
    Also when replacing the Front sight pins in you MUST put them in from the right side only( looking from the chamber end ) allso small end first.

  6. #6
    Gunco Rookie BushBack15's Avatar
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    Thanks for all sugestions when I get chance I'll do them. I've built 4 other rifles before this one but all barrels came with Extention. this is first time I've known that the Extentions were different and would mount barrel in other than 12:00 position. Actually I would proabley be ahead if I bought Barrel with exstention already fit to it . But since I have the parts from other builds I thought I'd try with what I had . money is little tuff right now and i hate to leave something I like undone. I owned SP1 Flat side was first AR I owned for several years and even the triangle front I liked, plus old longer stock fits me better even though M4 is great too. Still SP1 balances out for me better than what has been change over the years. Still like oldie but goodies.

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