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Magpul BUIS rear ap. very far left

Discussion in 'Black Rifle Forum' started by vettely, Feb 18, 2010.


  1. vettely

    vettely
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    Today my co-worker and I went to the range and zeroed are new Magpul BUIS sight set ups. Both of are rear sights wound up with the rear aperature very far to the left which seems unusual even though the POI is spot on.
    Anyone else have this issue with their Magpul sights??
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  2. Glocks&Ducs

    Glocks&Ducs
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    My rear was pretty far off when it came in the package, but I centered it prior to shooting and it zeroed pretty much in the center.

    Did you guys put your own rifles together? Or were they factory built? Are they the same brand? If I recall correctly, when sights are off like that, it can be an indicator that the barrel was improperly torqued.

    Are you using a magpul front sight also, or is there a front sight base on those rifles?
     

  3. coverdog

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    Front sight canted?
     
  4. vettely

    vettely
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    Both rifles are identical Rock Rivers and we did install govt profile barrels on each. The barrel nut was torqued to 30 ft lbs three times (using a torque wrench). Front and rear sights are Magpul's. Awhile back I recall another forum members rear sight was also over to the left.
     
  5. ArmoryDoc

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    Sounds like your barrel is off center and needs indexed back counter clockwise. I would put a witness mark on the barrel vs. barrel nut, loosen the barrel nut, rotate it just a touch then re-torque it. Recheck your witness mark to make sure you still have adjustment then resight it in.
     
  6. fivestar

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    I have a Smith and a Magpul rear site as well. I checked mine and it's off to the left as well. Not as much as yours, but clearly not centered either.
     
  7. RUSH2112

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    I'm new to all of this but it seems to me there's not a whole lot that could be wrong with the rear sight itself to require that much cranking.
     
    #7 RUSH2112, Feb 19, 2010
    Last edited: Feb 20, 2010
  8. GlockSupremacy

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    I will also say it is the front sight. I have an mbus and i centered it prior to installing it on my rifle.

    I only had to go two clicks right to get it sighted in, and it looks perfectly centered to the eye that way.
     
  9. faawrenchbndr

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    Since the barrel is located in the receiver with a pin, it looks like your FSB is canted.
    Has anyone else shot this rifle? If not, that would be my next step. Verify that the
    rear sight NEEDS to be adjusted like it is for zero. May be shooter error.
     
  10. HogGlocker

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    concur on all points post above...mine basically in the center.
     
  11. vettely

    vettely
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    Thats what we were thinking (that the barrel could not be off due to the pin). We installed both of our barrels exactly as the various installation instructions, includeing Brownells, described. As I said, both our rifles are almost exctly the same except I have the La Rue rail system and my friend has the Rock River rail system, all free float. It just seems odd that after independently zeroing our sights both rear sights are way to the left. What are the odds on that? Thanks on the input, we are going to keep dinking with our rifles/sights.
     
    #11 vettely, Feb 19, 2010
    Last edited: Feb 19, 2010
  12. Glocks&Ducs

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    It doesn't matter that there is a pin. If the barrel is over-torqued, it can cause the rifle to shoot to one side. More than a few people have complained of the problem on new rifles and the manufacturer fixed it under warranty. I think it was Bushmaster, but it may have been another company like S&W. I'm not saying that is definitely the cause of your problem, but I doubt it is the sights. Unless you can see that a sight was obviously made off center, it can't be the sights.

    It is either your barrels, or the handguards. Since both of you are having the exact same problem with rifles you guys built, I would have to say you assembled something improperly.

    Another possibility is that the optic is causing a visual illusion and it causes your rear sight to be that far off in order to zero. Have you tried zeroing the sights without the optic installed? When you were zeroing the optic, did it require a bunch of clicks to bring it in also?
     
  13. Glocks&Ducs

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    After looking around some, 30ft lbs is only the recommended starting point and you absolutely HAVE to use the correct grease, and three times is just a guide. If you don't, you can very easily over-torque it, and you also have to make sure to keep your torque wrench at a 90 degree angle to the tool. If you don't, even though it clicks or indicates a certain poundage, it is actually torqueing to a different value than is indicated.
     
  14. tbone86

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    Mine is also pretty far to the left, but I don't think its a big deal cuz my brothers metal rear sight (diamondhead is what he has) and his is pretty far to the right. As long as you're shooting accurately I don't think it matters.
     
  15. vettely

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    Yeppers, I torqued my barrel nut to 35 ft/lbs using moly grease, knowing that 80-90 was the max I figured that would be a safe range to prevent Over torquing. Probably wind up taking it apart and putting back together again to see what happens. The hand guard being a tad off would also seem to be the most likely but the La Rues seem to have a good quality mounting system. Having installed aluminum heads on my 350 I figured this would be a piece of cake.