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Thread: Canted FSB or out of spec upper ?

  1. #21
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    Well BCM said that it was laser sighted to within 3 clicks using a mil-spec carry handle and for me to try a mil-spec carry handle to see what the results are. Since I don't have a mil-spec carry handle I can send it back to them on my dime ($20 or so) to have them check it and make adjustments.

    My buddy has a Bushmaster carry handle but I don't know if that is mil-spec or not. I'm not really sure what to do at this point.

  2. #22
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    Quote Originally Posted by SA80Dan View Post
    If you want to try for perfection, remove the barrel and lap the upper receiver face using this sort of tool:

    http://www.brownells.com/.aspx/pid=2...R-LAPPING-TOOL
    Of all the junkass AR-15 hobbyist tools that they sell, the lapping tool is king of the hill. The steel that piece of shit is made from is softer than the 7075-T6 upper. Coupled with the fact that you are abrading the tool at the same time you are ****ing up your upper, exactly what are you squaring to what?
    Last edited by MarkG; 05-07-12 at 09:50.

  3. #23
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    Quote Originally Posted by 2arkba View Post
    Well BCM said that it was laser sighted to within 3 clicks using a mil-spec carry handle and for me to try a mil-spec carry handle to see what the results are. Since I don't have a mil-spec carry handle I can send it back to them on my dime ($20 or so) to have them check it and make adjustments.

    My buddy has a Bushmaster carry handle but I don't know if that is mil-spec or not. I'm not really sure what to do at this point.
    This info is correct (on them checking FSB's with a laser).


    In the past, we have seen BUIS's with bad clamping brackets (don't engage the receiver properly and are canted to one side or another).

    So using a known quality carry handle (like Colt) is a good way to check things out.

    C4

  4. #24
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    Quote Originally Posted by MK18Pilot View Post
    Of all the junkass AR-15 hobbyist tools that they sell, the lapping tool is king of the hill. The steel that piece of shit is made from is softer than the 7075-T6 upper. Coupled with the fact that you are abrading the tool at the same time you are ****ing up your upper, exactly what are you squaring to what?
    The front of the receiver face where it joins with the barrel. Its well known there are variations there. If you use the tool properly you are not ****ing up anything, you are literally shaving a fraction of a hairs worth of metal. Is it really worth doing? No in my opinion, but if you are going to quibble about having to adjust your sight off center, it'd be worth it to some.
    Dan

  5. #25
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    Quote Originally Posted by 2arkba View Post
    I'm not really sure what to do at this point.
    It looks like this is enough of a problem to you that the $20 for shipping is nothing compared to the ease of mind you will get in return. Just send it back, have them bless or fix it and be done with it.

  6. #26
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    Quote Originally Posted by rkba01 View Post
    It looks like this is enough of a problem to you that the $20 for shipping is nothing compared to the ease of mind you will get in return. Just send it back, have them bless or fix it and be done with it.
    BCM just sent me a return label so they can inspect it. that's quality customer service right there.

  7. #27
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    Quote Originally Posted by djmorris View Post
    SW-Shooter is on some big crusade to say that BCM is no better than DPMS, Olympic Arms, etc.

    Seems to me perhaps BCM got a bad batch of upper receivers. This problem has been reported a lot lately. In all honesty, it's small potatoes in comparison to the problems companies like DPMS and RRA see buddy.

    You are taking one thread and molding it to fit your incorrect observation. If you do a simple scan the last ten pages in the AR forums General & Tech, you'll find that there have been no less than 3 instances (TOS as well) of out of spec BCM products (uppers). That doesn't mean I said "go out and buy DPMS", what that means is BCM is having so QC issues lately. With the rush it's bound to happen.

    My point in the other non technical thread was that you should buy the best you can afford and become proficient with that. It's better to know your tool, than to sit there and admire it because you can't afford to shoot the darn thing. You took what I stated out of context.

    I am not on a crusade against BCM, but it's the community's responsibility to make everyone aware of the problems they are experiencing. Every manufacturer has produced an out of spec part(s) at one time or another. That doesn't make the brand crap. That is my only point.

  8. #28
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    I don't see a rear sight off center to be an issue..... maybe, if it's bottomed out all the way to one side.

    That's why we have adjustable sights on these things. If every AR had the adjustable rear sight perfectly centered, we could do away with the adjustability. But there are just too many connections and tolerances between the muzzle and the rear sight-- it would be impossible to get every sight perfectly centered:
    Front sight to barrel mounting (or):
    Front sight to rail mounting
    Rail to receiver
    Barrel to receiver
    Receiver threads
    Receiver face
    Barrel extension
    Barrel extension locating pin to slot in receiver face
    Barrel nut
    Rear sight to receiver mounting
    ..... not to mention, tolerances in the barrel itself with regards to concentricity and straightness.

    Even with the very highest quality parts, and let's say, held to 75% of the tolerances, there are still just too many joints to hope for perfection every time. The one pictured is not what I'd call a problem but I think it's very kind of BCM to take a look at it.

  9. #29
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    Quote Originally Posted by Ned Christiansen View Post
    I don't see a rear sight off center to be an issue..... maybe, if it's bottomed out all the way to one side.

    That's why we have adjustable sights on these things. If every AR had the adjustable rear sight perfectly centered, we could do away with the adjustability. But there are just too many connections and tolerances between the muzzle and the rear sight-- it would be impossible to get every sight perfectly centered:
    Front sight to barrel mounting (or):
    Front sight to rail mounting
    Rail to receiver
    Barrel to receiver
    Receiver threads
    Receiver face
    Barrel extension
    Barrel extension locating pin to slot in receiver face
    Barrel nut
    Rear sight to receiver mounting
    ..... not to mention, tolerances in the barrel itself with regards to concentricity and straightness.

    Even with the very highest quality parts, and let's say, held to 75% of the tolerances, there are still just too many joints to hope for perfection every time. The one pictured is not what I'd call a problem but I think it's very kind of BCM to take a look at it.
    I agree that there needs to be adjustments but the spec according to BCM is 23 clicks either way so I just wanted to make sure there wasn't anything messed up

  10. #30
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    I gotta tell you, I've got a Colt 6520 that's the same way. As in 6520 with a fixed carry handle. If you can sight it in within the range of adjustment, it's good. FWIW, I've got a mid length 14.5" BCM with the same offset. I aint worried. These guns are going to be way more out of spec when I'm done beating the snot out of 'em.
    Last edited by JPB; 05-08-12 at 23:42.

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