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Thread: Running out of Iron Sight Adjustment before zero is achieved.

  1. #1
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    Running out of Iron Sight Adjustment before zero is achieved.

    Hey Guys,

    Was teaching a class this past Saturday and at the beginning of each course we make sure all students have a 50 yd zero on their carbines. I had one student that could not achieve zero because his rear sight ran out of adjustment. He was about 4 inches left of center and the rear aperature was cranked all the way to the right. He custom built the upper himself and I'll list the specs below.

    BCM Flat top upper
    Weapon Outfitters 13.7 BA Hanson Bbl
    PRI Mk12 Handguard
    Surefire Socom Brake
    Troy Industries front and rear buis.

    I'm thinking that because the front sight is mounted on the rail, when he cranked down the barrel but that it's misaligned so when the handguard was installed it is not aligned concentric to the center of the upper. That's my guess as the front sight appears canted to the right slightly.

    Any insight is appreciated as I have yet to see this one in a class before.

    Moose

  2. #2
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    His rail was crooked or canted.

  3. #3
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    On that handguard the picatinny rail does not meet the upper. You need to use a straightedge to verify it is clocked correctly.

  4. #4
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    Who shows up to a class 8MOA off the bullseye? Do you often have people completely un-sighted-in when they arrive?

  5. #5
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    Probably had the optic zeroed, and tossed on a BUIS and figured it was good enough?

  6. #6
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    Quote Originally Posted by Auto-X Fil View Post
    Who shows up to a class 8MOA off the bullseye? Do you often have people completely un-sighted-in when they arrive?
    one of my friends takes lots of classes and it happens often with a new shooter.

  7. #7
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    use one of those laser line levels and run down entire top of the rifle
    I use those on ak's to get the cant out of the front sights

  8. #8
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    Happens all the time. Getting a rail properly clocked and indexed isn't hard, but alot of home builds end up being way off.

  9. #9
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    Quote Originally Posted by MOLON AABE View Post
    Happens all the time. Getting a rail properly clocked and indexed isn't hard, but alot of home builds end up being way off.
    Correct. I've found the best way to line a rail up to the upper receiver; (at least on my Midwest Industries quad rails), is to take a removable carry handle and attached it to the receiver rail and the rail itself; half on the upper rail and half on the rail. Next, tighten it down well and then tighten the jamb nut down with the carry handle still attached. Finally I install the anti-rotation screw/pin last but don't crank it down too hard, just a hair past snug with blue locktite is sufficient. Remove the carry handle and boom; the rail is aligned as close as humanly possible.

    To align newer M-Lok styled rails I align the barrel nut, gas tube, and upper receiver gas hole as close to perfect as possible. It usually takes 3-4 times of tightening, measuring, loosening, and retightening everything to get that gas tube in without binding at all on the sides of the teeth of the barrel nut while being aligned directly in the center of the receiver hole. Then I use the same process as described above with the carry handle for the final fine tune/rail alignment. It has worked every time for me with the most I've ever had to crank the rear site is 2-3 clicks in either direction to get zero'd. YMMV.

  10. #10
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    Quote Originally Posted by jmreagan View Post
    Correct. I've found the best way to line a rail up to the upper receiver; (at least on my Midwest Industries quad rails), is to take a removable carry handle and attached it to the receiver rail and the rail itself; half on the upper rail and half on the rail. Next, tighten it down well and then tighten the jamb nut down with the carry handle still attached. Finally I install the anti-rotation screw/pin last but don't crank it down too hard, just a hair past snug with blue locktite is sufficient. Remove the carry handle and boom; the rail is aligned as close as humanly possible.

    To align newer M-Lok styled rails I align the barrel nut, gas tube, and upper receiver gas hole as close to perfect as possible. It usually takes 3-4 times of tightening, measuring, loosening, and retightening everything to get that gas tube in without binding at all on the sides of the teeth of the barrel nut while being aligned directly in the center of the receiver hole. Then I use the same process as described above with the carry handle for the final fine tune/rail alignment. It has worked every time for me with the most I've ever had to crank the rear site is 2-3 clicks in either direction to get zero'd. YMMV.
    Did you notice what hand guard he is using? He'll have a tough time using a carry handle to clock it.

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