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Thread: Trouble with Mk18 zero

  1. #1
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    Trouble with Mk18 zero

    I'm out of ideas...... I've been trying to dial in my irons and am having a bit of an issue. I've drifted the rear sight right quite a way to the right trying to move my groups right. Yet consistently I hit 3-4 inches to the left. Its roughly the same place regardless of adjustment. I've tried different shooters with the same result. I thought it was just me but so far nobody who has shot it has made it group. The rifle is currently set up with Troy BUIS and I'm shooting independence 5.56. Anyone ever have issues that regardless of adjustments you can't walk your group in? The ammo groups in my 16 inch DDM4V5. Thanks in advance.

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    Quote Originally Posted by TylerD View Post
    I'm out of ideas...... I've been trying to dial in my irons and am having a bit of an issue. I've drifted the rear sight right quite a way to the right trying to move my groups right. Yet consistently I hit 3-4 inches to the left. Its roughly the same place regardless of adjustment. I've tried different shooters with the same result. I thought it was just me but so far nobody who has shot it has made it group. The rifle is currently set up with Troy BUIS and I'm shooting independence 5.56. Anyone ever have issues that regardless of adjustments you can't walk your group in? The ammo groups in my 16 inch DDM4V5. Thanks in advance.
    Try running the stock in the longest position and your eye farther from the aperture.

    I always zero with an aimpoint and then adjust the irons to the dot (stock all the way open and away from the aperture)

    I'd also let someone else shoot it.

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    All screws tight? Maybe a loose barrel? Or out of spec barrel or upper? Possibly canted rail?

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    Quote Originally Posted by themighty9mm View Post
    All screws tight? Maybe a loose barrel? Or out of spec barrel or upper? Possibly canted rail?
    Factory built DD Mk18..... I have only installed an AAC flash hider. That was done by a professional gunsmith. I would hope nothing is out of spec, but I definitely don't have this issue with my M4V5. I checked to make sure the sights were tight. All screws to the rail are torqued down properly. Flash hider is tight as well. I am trying to figure this out before a carbine class in June that I have. If I can't shake it down the upper will go back to DD. That's a last resort though.

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    Quote Originally Posted by TylerD View Post
    Factory built DD Mk18..... I have only installed an AAC flash hider. That was done by a professional gunsmith. I would hope nothing is out of spec, but I definitely don't have this issue with my M4V5. I checked to make sure the sights were tight. All screws to the rail are torqued down properly. Flash hider is tight as well. I am trying to figure this out before a carbine class in June that I have. If I can't shake it down the upper will go back to DD. That's a last resort though.
    It coulda been a Monday or Friday gun. Check to make sure the RIS 2 is aligned properly, and everything is square. Beyond that about your only possibility, is something on the rifle is not in spec or loose barrel. Perhaps you were resting the muzzle device on a sand bag? And you said multiple people were having the same issue?

    Loose barrel is not likely if all shots are grouping to the left. I think most likely the rail just is not squared up. If that's the case loosen all 6 screws, place a carry handle rear sight or other optic mount bridging the upper receiver and rail. Then retighten the screws in a like you would lug nuts on a wheel

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    Quote Originally Posted by themighty9mm View Post
    It coulda been a Monday or Friday gun. Check to make sure the RIS 2 is aligned properly, and everything is square. Beyond that about your only possibility, is something on the rifle is not in spec or loose barrel. Perhaps you were resting the muzzle device on a sand bag? And you said multiple people were having the same issue?

    Loose barrel is not likely if all shots are grouping to the left. I think most likely the rail just is not squared up. If that's the case loosen all 6 screws, place a carry handle rear sight or other optic mount bridging the upper receiver and rail. Then retighten the screws in a like you would lug nuts on a wheel
    I was shooting off of a backpack..... Rail was only thing resting on the back pack. I will take a look at the rail again tomorrow. I'll definitely take the advice and run with it as the rail had to come off for the install of the flash hider. I just know I have adjusted quite a few clicks to the right with no resolve and the gun groups like shit. I had a friend suggest running the rear sight all the way to the right and left then re-center and shoot again. I don't know what that would help but input would be good to hear. Thanks again

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    Quote Originally Posted by TylerD View Post
    I was shooting off of a backpack..... Rail was only thing resting on the back pack. I will take a look at the rail again tomorrow. I'll definitely take the advice and run with it as the rail had to come off for the install of the flash hider. I just know I have adjusted quite a few clicks to the right with no resolve and the gun groups like shit. I had a friend suggest running the rear sight all the way to the right and left then re-center and shoot again. I don't know what that would help but input would be good to hear. Thanks again
    You would know if the rail wasn't straight. Put an optic on it and shoot for groups. If you have to max the windage on the optic somethings wrong.

    If you can get a mount to go over the receiver/forearm gap then the rail is on straight.

    Edit: might want to witness mark the rear sight windage setting. Could be moving under recoil?
    Last edited by t15; 05-21-14 at 02:14.

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    Try a different ammo. The ammo may work in one gun but yours may not like it.

    Groups all over sounds like a loose barrel nut or damaged crown. My votes on loose barrel nut.

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    Quote Originally Posted by SpankMonkey View Post
    Try a different ammo. The ammo may work in one gun but yours may not like it.

    Groups all over sounds like a loose barrel nut or damaged crown. My votes on loose barrel nut.
    I may try to borrow a friend's rifle rest to see it I can eliminate human error from the equation as well. This may help tighten it up. I was shooting 100 yards on irons. However I can take my 16 inch gun and shoot 1 inch groups on a good day. Not saying I can't make a mistake but most days I don't shoot terribly.

  10. #10
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    For the record I have fired about 2K rounds of that ammo with no issues at all. You could simply have a bad barrel. Maybe the gunsmith jacked up the crown when he was changing the muzzle device?



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