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Thread: Help needed in sighting in.

  1. #1
    Gunco Member rudy's Avatar
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    Default Help needed in sighting in.

    I've assembled over 60 AR-15's so far, but this is my first flattop with BUIS.

    Here's my problem. I'm sighting in at 25 yards. I was quite low the first couple of rounds so I started screwing down the front sight post. The post is now bottomed out and I'm still 2-1/2" low!

    My rear sight is a Midwest Industries. It seems to work fine, and there are no elevation adjustments possible.

    The upper is a flattop made by Superior Arms in Iowa. The rail seems to be the same height as other flattops that I've compared it to.

    The barrel is an M16A2. It was shortened to 16.25" and the original gasport was used to keep the rifle's longer sight radius. The gas port was opened slightly to allow operation in subzero weather.

    The FSB is military issue.

    I need to know if the M16A2 and the M4 carbine use different front sight bases? If so, could I have the wrong one on my rifle?
    "419"
    "It is foolish and wrong to mourn the men who died. Rather we should thank God that such men lived." - General G. Patton Jr.

  2. #2
    Gunco Member campperykid's Avatar
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    Not a complete answer but a start.
    There are two basic FSB heights: One for detachable carry handles/BUIS and one for the old style A2 built-on handles. Try this site for more details:
    M4Carbine.net

    There are some very experienced people over there. The main focus is work guns , but hobby shooters and armed citizens are welcome.

  3. #3
    Gunco Rookie Orion's Avatar
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    Smile

    Yes there is a diferent front sight base for flat tops. The A2 is higher. You should have an "f " marked front sight base for a flat top. Dont dispaire there are replacement sight posts available for this. Search and you can find them. They are for this very thing.

  4. #4
    Gunco Rookie deanathpc's Avatar
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    Quote Originally Posted by Orion View Post
    Yes there is a diferent front sight base for flat tops. The A2 is higher. You should have an "f " marked front sight base for a flat top. Dont dispaire there are replacement sight posts available for this. Search and you can find them. They are for this very thing.
    hmmm I just bought my sites from the gun show this past weekend. They were attached to a flat top upper so I'm assuming they are designed for such. I don't see a "f" anywhere though.. I don't have barrel for mine yet as I am still building / assembling it so I won't know for sure for some time just how accurate it is. Makes me wonder if I got a bad deal now after reading this post..

  5. #5
    Gunco Good ole boy tanvil's Avatar
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    Does your front sight slide and pin on the barrel or is it machined for a rail?

  6. #6
    Hardened Member 1ak2b's Avatar
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    also remember that the 8/3 setting is 2 clicks up on an M4 with the military zero target.

  7. #7
    Hardened Member 1ak2b's Avatar
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    I gotta watch this crap. hell this is a 1 year 8 month old thread...................

  8. #8
    Gunco Rookie deanathpc's Avatar
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    Quote Originally Posted by tanvil View Post
    Does your front sight slide and pin on the barrel or is it machined for a rail?
    mine is matched for a rail. guy sold it to me as a set. Maybe I shoulda researched a little more before buying into the deal he offered?

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