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Thread: Help determining if my FSB is canted?, Newbie post.

  1. #11
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    Quote Originally Posted by C4IGrant View Post
    I know what is wrong with your FSB, you are drinking STROH's!


    Sorry, couldn't hellp myself. Off to the corner I go.





    C4
    That was at deer camp...my brother in law drinks it, not me lol.

    By the way, I purchased the lower from you last earlier this month, lol small world

  2. #12
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    Quote Originally Posted by SPM14430 View Post
    Did you check that the FSB was perfectly straight before you had the work done on it? I have in the past received a factory BCM upper with a slightly canted FSB. It's unlikely the smith made an error reinstalling the FSB.

    Another possibility is that the barrel nut may be over torqued. Did the smith remove the barrel at any point?

    13 clicks is within spec. But if it really bothers you, an alternative is going with a low pro gas block and floating a midlength rail over it.

    No because it came without handguards from bravo and I didn't think to measure it when I first got it anyhow.

  3. #13
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    The DD rail uses a proprietary barrel nut.

    Quote Originally Posted by SPM14430 View Post
    Did you check that the FSB was perfectly straight before you had the work done on it? I have in the past received a factory BCM upper with a slightly canted FSB. It's unlikely the smith made an error reinstalling the FSB.

    Another possibility is that the barrel nut may be over torqued. Did the smith remove the barrel at any point?

    13 clicks is within spec. But if it really bothers you, an alternative is going with a low pro gas block and floating a midlength rail over it.



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  4. #14
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    Quote Originally Posted by Iraqgunz View Post
    Since that is the factory FSB, and you only moved it 13 clicks and based on your photo then I wouldn't be concerned.
    IG, how much is too much? I'm in similar shoes. My BCM upper appears to be canted slightly left. A Troy rear (which I no longer use) took 40 clicks but was still within the adjustment range. BCM (with typically awesome CS) offered to take a look for me but I'm not sure it's worth the trouble... it's my HD and farm rifle. Shots beyond 50 yds uncommon... beyond 100 unlikely. I can still hit minute-of-coyote at those ranges just fine and I otherwise love the shit out of that upper.

    So for me and the OP... at what point should a cant make you stress out? If you're windage is off by "x" at 100 yards, for example?
    Last edited by rackham1; 11-29-11 at 18:44.

  5. #15
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    If you are concerned about it send it in. If I think I think real hard when I BZO'd my issue M16A2 rifle, my rear sight was moved left about 9 clicks and my front sight post was down about 3.

    Excessive to me would maxed out left or right and still not being able to get a good zero.

    I also use a Troy front and rear sight. In this case I would put an A2 carry handle on the gun and then PROPERLY attempt to zero it.


    Quote Originally Posted by rackham1 View Post
    IG, how much is too much? I'm in similar shoes. My BCM upper appears to be canted slightly left. A Troy rear (which I no longer use) took 40 clicks but was still within the adjustment range. BCM (with typically awesome CS) offered to take a look for me but I'm not sure it's worth the trouble... it's my HD and farm rifle. Shots beyond 50 yds uncommon... beyond 100 unlikely. I can still hit minute-of-coyote at those ranges just fine and I otherwise love the shit out of that upper.

    So for me and the OP... at what point should a cant make you stress out? If you're windage is off by "x" at 100 yards, for example?



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  6. #16
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    Quote Originally Posted by Iraqgunz View Post
    If you are concerned about it send it in. If I think I think real hard when I BZO'd my issue M16A2 rifle, my rear sight was moved left about 9 clicks and my front sight post was down about 3.

    Excessive to me would maxed out left or right and still not being able to get a good zero.

    I also use a Troy front and rear sight. In this case I would put an A2 carry handle on the gun and then PROPERLY attempt to zero it.
    Gotcha, that's good advice. I guess what I getting at though is it's not the adjustment range that concerns me, but how far off the windage will be downrange from your zero. That's basically what a cant does, right? Zero at 50, then your windage is off at 100... or zero at 100, then your windage is off at 50... am I wrong?

    For me, zero'd windage at 50 but 1-inch right at 100 is within my needs... no concerns for me. Just wondering what the rest of the group would consider acceptable for a HD rifle (understanding that long-range, competition, etc. are a different story).

  7. #17
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    Quote Originally Posted by markm View Post
    That flip up, grabasstic excuse for a sight is more likely to be out of whack. Is that one of those Troy creations? They're ALWAYS popping up on the forums with lots of windage required.

    And I agree... the windage is acceptable.. even with the poo sight.
    never push a wrench...

  8. #18
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    Quote Originally Posted by rackham1 View Post
    IG, how much is too much?
    Not IG, but excessive windage is defined in the last pages of the milspec, I'd have to go pull up my copy to get the verbiage though.

    ETA:
    The MIL-R-63997B (AR) Amendment 4 31JUL93 which covered the M16A2 at that time specifies that with the rear sight set +/- 5 clicks (0.5 MOA) from center all shots of a ten round group of M855, having a horizontal and vertical SD of between 3.4 and 4 inches at 600 yards, must fall into a roughly rectangular target 17.6" tall and 11.6" wide set at 100 yards.

    http://www.ar15.com/content/manuals/m16a2milspec.pdf

    the M4A1 JAN94 spec calls for +/- 12 clicks (0.68 MOA) with the same but at a 22" by 16" 100 yard target.

    http://www.ar15.com/content/manuals/m4a1milspec.pdf
    Last edited by Tweak; 11-29-11 at 21:56.

  9. #19
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    Tweak,

    Based upon what you have seen thus far. Do you think that the rear sight seems to be adjusted "excessively"?

    If he can get it to zero properly at 50 yards and maintain good groups at longer distances wouldn't that mean that the FSB is fine?

    Quote Originally Posted by Tweak View Post
    Not IG, but excessive windage is defined in the last pages of the milspec, I'd have to go pull up my copy to get the verbiage though.

    ETA:
    The MIL-R-63997B (AR) Amendment 4 31JUL93 which covered the M16A2 at that time specifies that with the rear sight set +/- 5 clicks (0.5 MOA) from center all shots of a ten round group of M855, having a horizontal and vertical SD of between 3.4 and 4 inches at 600 yards, must fall into a roughly rectangular target 17.6" tall and 11.6" wide set at 100 yards.

    http://www.ar15.com/content/manuals/m16a2milspec.pdf

    the M4A1 JAN94 spec calls for +/- 12 clicks (0.68 MOA) with the same but at a 22" by 16" 100 yard target.

    http://www.ar15.com/content/manuals/m4a1milspec.pdf



    Owner/Instructor at Semper Paratus Arms

    Facebook: https://www.facebook.com/SemperParatusArms/

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  10. #20
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    I didn't say it was excessive, I said the milspec defined excessive since it sounded like he wants a quantitative answer.

    If it was my rifle, yes, that's excessive, I adjust mine as close to zero as possible.

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