Questions for the AR-15 gurus

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  • thompal

    Master
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    0   0   0
    Sep 27, 2008
    3,545
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    Beech Grove
    Couple of quick questions that I'm sure a lot of you can answer:

    I just got a new AR-15 BCG, and the bolt seems awfully tight in the carrier. If I stand it on the bolt, the carrier isn't close to sliding down. I've checked for burrs or ridges, but it all looks OK. Is this normal for a new, never fired BCG? My other (WELL-used) BCGs are much looser, and the carrier slides easily if you stand it upright on the bolt. It's been so long since I had a brand new one that I honestly don't remember.

    Secondly, I've got a different upper that has an unmarked FSB on it. My others are F marked. What different bases are there, and is there an obvious difference?
     

    Opie

    Sharpshooter
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    61   0   0
    Feb 2, 2013
    525
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    Evansville
    IF the carrier slides down when bolt standing, the rings are worn. You don't want it to close on its own weight.

    F marked bases are a fraction taller, if the gun zeros properly without having a loose front sight then it is a non issue.

    Hope that helps!
     

    Hohn

    Master
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    Jul 5, 2012
    4,444
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    USA
    "F" marked based are designed to be used with flattop rifles rather than integrated carry handle rifles. If you measured from the center of the barrel axis to the top of the sight post, you'd find the F marked to be a tiny bit taller as Opie indicated.

    As long as the bolt and carrier are functioning OK, tight isn't a problem. My DD bolt and carrier are similarly stiff. As long as the action is smooth and continuous (even if stiff) it's GTG.
     
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