Flip up sight problems

Discussion in 'AR-15 Discussion' started by FearTheFree7, Jul 3, 2012.

  1. FearTheFree7

    FearTheFree7 New Member

    145
    0
    0
    I've been having problems sighting in my AR. The first set of flip up sights I had on it were pro mags and they were shooting way high even with the front post all the way up. So I purchased magpul sights. Those shot way low. I checked to make sure the gun was level and it was. Anyone have problems with this before? I have a bushmaster xm15-E2S.
     
  2. Jpyle

    Jpyle New Member

    4,828
    0
    0
    Post a pic so we can have a look but my first thought is that you have "same plane" sights mounted on a gas block. Is the front sight on a gas block or on the hand guard rail? If on a gas block, is it taller than the rear sight?
     

  3. Quentin

    Quentin New Member

    7,551
    1
    0
    In addition to what Jpyle said, BUshmaster uses commercial height sights, not milspec. If you're mixing a BM front with a milspec height rear you have to unscrew the front post so much it flops around. BM does sell a $6-7 tall front sight post to fix this. Can't remember what they call it but Colt was in the name. I had to put one in my ArmaLite to get it to zero with a milspec rear.
     
  4. purehavoc

    purehavoc New Member

    4,799
    2
    0
    I put a full rail hand guard on mine as I originally had the FSB on it and my sight was way off after putting the troy handguard on ,my magpuls were shooting way way high and I literally have it unscrewed most of the way out but finally got it ,my rear sight is all but 1/8" from the right . Im not going to try to move the rail around to adjust its lined up perfect with the receiver . its set and Im leaving it there . not all brands are the same height and hopefully the magpuls will work for you .
     
  5. FearTheFree7

    FearTheFree7 New Member

    145
    0
    0
    They front sight is on the gas block and they look to be on the same plane.
     

    Attached Files:

  6. Dillinger

    Dillinger New Member

    23,972
    1
    0
    Anyone have AutoCAD or software that can draw a couple of linear lines on that picture to compare the sights in relation to the bore axis?

    It appears, and I took a copy and was just playing with it on the laptop here with a cut and crop program, that your sights are not in line with the bore axis and I think that might be contributing to your problem.

    Do you have a micrometer by any chance? Where you can get the measurements of the two different front sights and see what the difference is in post height?
     
  7. mountainman13

    mountainman13 New Member

    11,488
    0
    0
    Not anymore. I'm done with auto-cad sorry. You may be able to use a carpenter square to get a pretty good idea.
     
  8. SSGN_Doc

    SSGN_Doc Well-Known Member

    6,924
    50
    48
    You won't want to run that front sight on your gas block. MagPul advises thatthese were made to be run on handguards. Gas blocks can get hot enough to melt the sight.
     
  9. mountainman13

    mountainman13 New Member

    11,488
    0
    0
    Did not know that. Good to know. Ty
     
  10. Dillinger

    Dillinger New Member

    23,972
    1
    0
    Yeah, I haven't had a license for it in years. Just messing around it appears the front sight is high in relation to the rear sight and where I assume the dead center of the barrel should be, forcing the front of the barrel down.

    I think you might just not have the correct sights for your application. Quentin mentioned BM doesn't use mil spec above. Are the Magpul sights mil spec?

    JD
     
  11. mountainman13

    mountainman13 New Member

    11,488
    0
    0
    Idk If they are or not.
     
  12. Quentin

    Quentin New Member

    7,551
    1
    0
    Very true! And even if you don't get the gas block that hot, odds are the front MBUS is too low to zero on the block. Why not mount it on the rail and try to zero, that should work.
     
  13. MikeJK

    MikeJK New Member

    1,427
    0
    0
    W/ all the "my sights don't line up" threads that end up being the fault of a half ass railed gas block you'd think people would stop purchasing ARs w/ those ugly railed gas blocks.
     
  14. purehavoc

    purehavoc New Member

    4,799
    2
    0
    Here is what im finding out magpul gen 1 and gen 2 are different heights make sure you arent mixing them.
     
  15. jg3

    jg3 New Member

    95
    0
    0
    I second that!!...man those things are so ugly!!!
     
  16. jg3

    jg3 New Member

    95
    0
    0
    I have autocad...any of you guys drafters too?! I will lay it out later tonight and post a pic
     
  17. lilbailnick

    lilbailnick New Member

    98
    0
    0
    My thoughts for the folding BUS in relation with the gas block is that I'd prefer the lower profile GB as opposed to a same plane GB. It does in some cases look ugly, but on my STAG M3 has the lower pro GB and with Troy's folding front sight for lower plane GB looks awesome to me when using Troy's folding front sight for lower-pro. I love the feature for which it's intended to do and that having more options for either absolute co/witness & clear view. But in the end I don't at all like that the same plane GB. I'm more in favor about how I like the lower GB as opposed to the A-frame tower or high-Pro. So with whatever sights you do get
     
  18. Quentin

    Quentin New Member

    7,551
    1
    0
    Yeah my first AR build had an ArmaLite upper with the low rail gas block so I got ArmaLite's clamp on FSB that got it to the right height for their own rear sights. Trouble was they used the commercial height like Bushmaster, DPMS, Oly and lots of others - not the milspec height for a flat top (thus the F marked FSB that Colt, BCM, DD, LMT, Noveske and the better ARs use).

    It was frustrating trying to zero the irons until I finally found out about BM's tall front post for Colt height rear sights and now I can use any milspec rear sight. Funny, that one thing opened my eyes to going with quality ARs from then on. If that little thing was wrong, what about the really important things!

    Could be the same thing going on here but I bet moving the front MBUS to the quadrail will fix the problem quick, both sights should be milspec height then.


    ETA:

    The opposite can happen too - if you get a BM carry handle or rear sight and try to use it with a milspec front you have to crank the sight post way down into the FSB and maybe get it to zero. At least with a BM carry handle you can reindex it about 14 clicks below 6/3 to raise the peephole to milspec height.
     
    Last edited: Jul 4, 2012