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AR15 Gas Block Flip Up Sight Alignment

Discussion in 'Maintenance & Gunsmithing' started by cascadianliberty2012, Jan 27, 2014.

  1. cascadianliberty2012

    cascadianliberty2012 DPR Portland Well-Known Member

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    Hey everyone,
    I just finished my 80%-lower AR15 build and shot it for the first time today. Shoots great, however, I can't seem to get the front Magpul flip-up sight to (on top of a Thor's Hammer gas block) to line up with the Magpul rear flip-up sight. Is there a trick to getting these lined up perfectly? Simply "eyeballing" it doesn't seem to work so well in this application. Attached is a pic. Also, my fore-end is a quad rail, and have a standard gas system.

    Thanks!

    (I have no idea why the picture is upside-down when it got uploaded, but you can see what my situation is)

    20140127_215219.jpg
     
  2. Greenbug

    Greenbug Bend Well-Known Member

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    Take the front sight off the gas block and put it at the end of your fore end rail. This way it should be at the same height as your rear sight and you get the added bonus of not melting your plastic back up sight when you cook off a bunch of rounds and overheat your gas block. It's hard to see in your picture but the gas block picatinny is probably lower than your fore end picatinny and that is probably the source of your problem.
     
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  3. Velzey

    Velzey Estacada, Oregon Gunsmith Gunsmith Bronze Vendor Bronze Supporter

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    You need a gas block front flip sight.

    YANKEE HILL MACHINE CO., INC. - GAS BLOCK FRONT FLIP SIGHT
    Brownells # 100-002-089wb
     
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  4. parallax

    parallax eugene, or-gun Bronze Supporter Bronze Supporter

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    what Velzey sez:.. I am pretty sure there are 2 different height flip up front sights.. you need the one designed for the gas block.
    found out the hard way myself by buying the wrong one for my rifle..:(
     
  5. cascadianliberty2012

    cascadianliberty2012 DPR Portland Well-Known Member

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    Height isn't the issue, it's the left-right alignment that is the problem.
     
  6. Velzey

    Velzey Estacada, Oregon Gunsmith Gunsmith Bronze Vendor Bronze Supporter

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    Oh geeeZe sorry! That's what I get for skimming.

    I use a machinist 24" steel ruler for that. Pretty easy to eyeball it square . You can lay the ruler on the rear picatinny and just extend it all the way out over the front block. Really easy to tell when it's out of square.
     
  7. 308

    308 ΜOΛΩΝ ΛΑΒΕ ΜOΛΩΝ ΛΑΒΕ Platinum Supporter Silver Supporter

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    Loosen the setscrews on the gas block slightly and tap it right or left to get your windage correct with both sights set to the center position.
    Once it's perfect, pull one setscrew at a time and blue loctite it in place. Red loctite is nightmare if you ever need to pull the screws gain.
     
  8. bellarum

    bellarum beaverton Well-Known Member

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    Like Greenbug said: no mater what you have a magpul sight mounted in the wrong position. You should move it back and onto your tube where it won't melt. Same plane as the rear is ideal if your float tube and flat top rails line up. There are tons of threads here and there about NOT mounting magpul sights on gas blocks. Be careful if you do move your gas block to compensate as to not get the gas holes out of alignment.
     
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  9. cascadianliberty2012

    cascadianliberty2012 DPR Portland Well-Known Member

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    So never put a sight on a gas block? I've never heard that before. I suppose I could move it back to the quad rail, but I think it's weird a gas block would have a rail for a sight when the sight could melt. I bought these parts from Curt's in Milwaukee, and doubt they'd send me wrong... thoughts?
     
  10. Nwcid

    Nwcid Yakima and N of Spokane Well-Known Member

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    That is NOT what has been said. It is being said Magpul sights are NOT designed to take the heat on a gas block.

    http://store.magpul.com/product/MAG247/44
    NOTE: Cannot be mounted to a railed gas block due to excess heat issues.
    Front MBUS must be mounted to a railed fore end on the same plane as the receiver rail. Because of this the sight is also not compatible with MOE Hand Guards.


    Metal sites are no problem.

    Also there are 2 different height sights. First is meant to be mounted to the forward end of the rail, which is what ALL Magpul are. The other is taller and meant to be mounted on the railed gas blocks.

    These are not thoughts, they are facts.

    Here is just one example, http://www.midwestindustriesinc.com/index.cfm?fuseaction=category.display&category_ID=79
     
  11. cascadianliberty2012

    cascadianliberty2012 DPR Portland Well-Known Member

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    I think that could have been said in a little nicer of a fashion, but I do appreciate the information and direct quotations from a primary source.

    I moved the front sight onto the front end of the rail, but am now experiencing another issue... The quad rail I have mounted is slightly canted clockwise, so it doesn't perfectly line up with the rail on the upper receiver. I can't seem to get it straight and I've tried remounting it, moving the gas block/ring, but to no avail.

    Any ideas of how to get this to work right so the front sight lines up? I must say though, the front sight is now lined up "better" than before, but now it is just on an angled rail.
     
  12. erudne

    erudne The Pie Matrix PPL Say Sleeping W/Your Rifle Is A bad Thing? Bronze Supporter

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    did you spend $100 on the front sight?
     
  13. cascadianliberty2012

    cascadianliberty2012 DPR Portland Well-Known Member

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    $100 for both front and rear. Magpul flip-ups.
     
  14. Nwcid

    Nwcid Yakima and N of Spokane Well-Known Member

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    I did not know facts were being rude. I was also being clear that you had misunderstood what the others had said.

    The red are highlights of the pertinent parts of the copied part of the link the directly addressed your info.

    You had asked for opinions so I simply stated what I had posted was fact not opinion..........
     
  15. erudne

    erudne The Pie Matrix PPL Say Sleeping W/Your Rifle Is A bad Thing? Bronze Supporter

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  16. cascadianliberty2012

    cascadianliberty2012 DPR Portland Well-Known Member

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    Interesting, but that isn't the problem. The rail, or something relating to the fore-end quad rail is...
     
  17. Nwcid

    Nwcid Yakima and N of Spokane Well-Known Member

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    There are a couple different ways of mounting railed handguards. Depending on what style you have you might have to loosen or tighten the barrel nut or barrel nut replacement to make the rails line up. That is one of the arguments for monolithic rails.

    Also your expectations may be to high, not saying that is the case though. These style of sights and the mounting options are for BACKUP as the name MBUS "Magpul Back Up Sights" imply. They are meant to be MOM, Minute Of Man, at reasonable distances. They are not intended for precision shooting. Just like the guys that run race guns have short radius open sights mounted on the side of their scopes they are meant for quick and dirty. If you want precision then you need the proper sights and proper mounting.
     
  18. samuelm16

    samuelm16 se pdx Well-Known Member

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    I would ditch that gas block and get a clamp on yankee hill flip up gas bolck front sight it works really well on mine
     
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  19. bellarum

    bellarum beaverton Well-Known Member

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    If you have a removable handguard, scope mount, or other similar picatiny attachment that is a few inches long you can loosen your handguard, bridge the top rail of your handguard with the rail on top of your upper receiver with it and tighten it down. Doing this will keep them in alignment while you re tighten the nut. That's about as close as you are gonna get.