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Thread: sight alignment problem

  1. #11
    Join Date
    Aug 2007
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    PA
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    Had a similar issue with a recent 10.5" LMT build I did; when sighted in, the rear BUIS apeture was biased significantly to the right and being an anal SOB, I didn't like it. Figured since the rear was off to the right, the barrel was biased to the left when the nut was tightened down. So, took everything apart and placed a really thin shim between the barrel and receiver so when tightened and torqued, the barrel would not sit in the receiver, 'pointing' towards the left as much. Went back to the range and sighted in, and voila, the rear BUIS apeture is perfectly centered - guess I guesstimated the correct amount of 'shim' to nudge the barrel. BTW, I did check the FSB and it wasn't canted, so figured it was the way the barrel was 'sitting' in the receiver.

    I too don't think it's the BUIS - it was nice of MI to send out another BUIS to try but in all likely hood, you still may have that rear apeture off to the side. If you're still not on target with the apeture pushed to the limit, you'll either have to shim the barrel with something 'substantial' or send the receiver back.

    Dave.
    Last edited by flyfishdave; 05-06-08 at 17:19. Reason: edit

  2. #12
    Join Date
    Apr 2007
    Location
    FL
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    This is a very common issue, and is regularly beaten to death.
    99% of the time the issue is not with the sights (I just made that statistic up, in case anyone wants to know my source).
    The issue, as touched on above, is the front sight.
    It is either the loaction of the front sight on the barrel itself, or the barrel is shifted behind the barrel nut, sometimes due to improper torque, incorrect placement of the witness pin in the barrel extension, or canted front sight (common with DIY non-pinned FSBs).
    There are several methods to fix the issue, from tapping the front sight in the opposite direction of the bias to retorqueing (I think I just made that word up).
    Here is an old post by gotm4 that's worth locking away in the ol' memory unit:
    Quote Originally Posted by gotm4 View Post
    Many times you can put the upper receiver in a block (in the vise) and twist the barrel within the upper receiver the way you need it to go. If it's hitting to far to the right, twist the barrel to the right.

    I usually just loosen the barrel and retorque it. This problem many times comes from people using barrel blocks (instead of upper blocks) to hold the barrel as they torque down the barrel nut to the receiver. I can also come from overtightened used a vice receiver block.

    If it hits too far to the left, they probably overtightened using barrel vise blocks.

    Sometimes a new barrel extension indexing pin will fix it, sometimes it requires a new upper receiver.

    I would like someday to make a jig that holds both the upper receiver and the barrel perfectly still while the barrel nut is torqued.
    gotm4- if you have any issue with me posting this, just let me know and I will pull it. Then again, I guess if you have an issue with it, you will just pull it yourself .
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  3. #13
    Join Date
    Dec 2006
    Location
    Commonwealth of Virginia
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    I had the same issue happen to me during Basic Training. Except the M-16A1 I was using was made by General Motors' Hydramatic Coproration (it still had the solid buttstock floor plate). I personally think that it may have had a twisted barrel.

    Great to know that MI stands behind their products!!
    We must not believe the Evil One when he tells us that there is nothing we can do in the face of violence, injustice and sin. - Pope Francis I

  4. #14
    Join Date
    Jun 2006
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    Colorado
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    Quote Originally Posted by Blitzking View Post
    On the new PK firearms upper, I attached a Midwest Industrys rear pop up sight. I finally took the scope off of the gun and decided to sight in the Iron sights. I had to adjust the sights all the way to the left just to get close to the target. I'm still not on target. Is my sight a POS or is something not right with the aligment of the upper? Anyone have a fix?

    I have a feeling that the issue is not the rear sight (made by M.I.) and probably not PK Firearms.

    I received an upper receiver from PK Firearms a few months ago, it sat in the safe until a couple weeks ago when I finally received the lower receiver.

    I put a Troy Ind BUIS (which was on a Colt LE6920 and was sighted in, the Troy Ind BUIS was as perfectly centered as a shooter could hope for) on the upper I received from PK and sighted the gun in. I have excessive left windage on the rear back up iron sight.

    Long story short. 2 - 3 years ago I purchased a barrel from a vendor made by Company X. I installed the barrel on a Stag Arms / CMT upper and put a LaRue BUIS on the upper. I had excessive left windage. I put a Troy Ind. BUIS and had the same problem.

    I contact Company X and they blame it on the CMT upper. After 3 trips back to Company X's factory, they finally replace the CMT upper with one of their uppers. They also give me a new barrel. After sighting in the new barrel / upper I notice that the rear sights are still zeroing to the left, just not as excessive as before.

    I order a barrel received (both barrel and receiver are made by Company X) and after zeroing the upper with a Troy Ind BUIS that was dead center on a Colt LE6920, I notice that the upper has excessive left windage.

    I was going to contact PK Firearms about the problem, but I've been tied up for the last couple weeks. Hopefully I can contact PK Firearms before the end of this week.

    I don't think the problem is with the Midwest Industries rear sight or PK Firearms, I'm guessing that the problem is with the way Company X assembles their upper receivers. I'm assuming / guessing that your upper was made by the same company has made my current upper and the other upper I was having problems with.

    Could you PM me the manufacturer of the upper receiver and barrel (along with barrel cofiguration - ie. 16" Mid-Length, 14.5" M4 barrel, etc) that you are having problems with. It would be greatly appricated.



    Thanks,




    S/F,
    Jeff

  5. #15
    Join Date
    Oct 2007
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    Small update-

    I was instructed by the fine folks at LMT to ship the upper back to have it inspected. They were pretty helpful over the phone. I'll post back when the upper gets back to me.

    -Rich

  6. #16
    Join Date
    Oct 2007
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    Got the upper back from LMT. The front sight was in fact canted. The reason for this is still unknown- I didn't get a response back explaining what was going on with the upper. I'm assuming the upper was zeroed at a decent range as the rear sight has been moved from my previous setting- which was far to the left. Also, while co-witnessesing the Aimpoint, the front sight now appears at the center-bottom of the tube.

    Now to take it to the range and verify the zero.

    -Rich

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