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Thread: Strange Issues - BCM even baffled

  1. #51
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    Who ever won, its something I looked at multiple times but some how evidently never got set correctly as it was up there on my list of probables as well.

    If I talk to them again, I may ask if the dimple was off and causing that or what it was as this is the first in 30+ rifles I've built that I've had this happen.

    Just like a Match DQ, its bound to happen to everyone at least once in their life. Guess it was my turn on the "way to go dumbass" train.

  2. #52
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    I've had at least a couple factory assembled uppers with the gas tube binding in the gas key, for various reasons including a misaligned gas block. Sure, you can 'tweak' the gas tube to get it kind of right, but I'd rather have everything lined up so that a straight gas tube works. I ended up sending an upper back to a very highly regarded mfg to correct their misaligned gas block, and it was for this reason. The gas port wasn't blocked at all but it put enough angle on the gas tube to cause some binding...not something I'm ok with.

  3. #53
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    Quote Originally Posted by Boba Fett v2 View Post
    No way, man. I beat you to it!

    Several people mentioned the GB alignment before I did. Was merely a joke.



    C4

  4. #54
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    FWIW- TM 9-1005-319-23&P allows for tweaking of the gas tube after installation into the upper by use of a flat tip screwdriver.

    Quote Originally Posted by krichbaum View Post
    I've had at least a couple factory assembled uppers with the gas tube binding in the gas key, for various reasons including a misaligned gas block. Sure, you can 'tweak' the gas tube to get it kind of right, but I'd rather have everything lined up so that a straight gas tube works. I ended up sending an upper back to a very highly regarded mfg to correct their misaligned gas block, and it was for this reason. The gas port wasn't blocked at all but it put enough angle on the gas tube to cause some binding...not something I'm ok with.



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  5. #55
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    Quote Originally Posted by jwfuhrman View Post
    Who ever won, its something I looked at multiple times but some how evidently never got set correctly as it was up there on my list of probables as well.

    If I talk to them again, I may ask if the dimple was off and causing that or what it was as this is the first in 30+ rifles I've built that I've had this happen.

    Just like a Match DQ, its bound to happen to everyone at least once in their life. Guess it was my turn on the "way to go dumbass" train.
    I suspect the dimple was not off but the barrel was. that is if the dimple was drilled before the barrel was installed...

    it's not unknown for BCM to have the front sight base canted a bit to the left from the factory. that's been discussed here and I've had one myself...
    never push a wrench...

  6. #56
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    I always build mine so that the gas block to barrel alignment is as perfect as possible and never use the gas tube to determine gas block alignment. I use drill rod to make sure the barrel nut/upper receiver alignment is perfect as well. You can always tweak a tube afterwards (as IG brought up) using a stripped carrier as a guide. But what happens when the tube gets replaced? If you have a set screw block thats been "tuned/tweaked" to get the tube straight, or you have "adjusted" the barrel nut for better alignment, now you are back to square one...

    No 2 gas tubes are alike...

  7. #57
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    Strange Issues - BCM even baffled

    This is why I scribe very small witness/timing lines on my barrel and gas blocks before installing. It's a good way to check dimple alignment, as well as port to port concentricity/alignment. A few measurements...even if closely eyeballing it, and you can put appropriate marks that will let you know if you're aligned or not before tightening with rockset or pinning.

    As IG mentioned, the GB port is several times larger in size (probably 3-4 times) that the barrel port. So even rough measurements and scribes, or pencil marks, will get it right every time.

    Aligning off of the tube isn't always a good idea to check port to port alignment, etc. a gas tube could be slightly tweaked, or even the tube hole could be drilled at a slight angle not perpendicular to the facing of the gas block.

    Just my method...and I've never had any issue with dozen or so BCM middle builds. They shoot wolf, Tula, and light ass plinking handloads with nothing more than a standard carbine spring and H buffer. Thousands and thousands of rounds through many of the builds and never a hiccup!

    Careful planning and attention to details pays off. Even if it takes you several hours to build an upper "perfectly".

  8. #58
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    I use a straight edge to put masking tape down straight over the center of the gas port to the tip of the barrel. I then take a Sharpie marker and draw a line on the edge of the tape giving me a straight center line from the hand guard "lip" to the muzzle. Then I slide the gas block on and use the line to make sure the block is plum. If the block requires dimpling or drilling then I verify alignment using light shined down the gas port (it will show a "spot" on the inside of the barrel. If the spot is symmetrical than you are GTG. A quicker easier check is a quick shot of brake cleaner. The Sharpie is easy to remove and leaves no marks...

  9. #59
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    Isn't it great having the internet.....if it were 1992, things would be a lot harder to fix.

  10. #60
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    Finally got home from Pro/Am 3gun and had a chance to go pick it up from my FFL(for some reason they required it to be shipped to FFL even though I sent it in for repairs). But I shot some of everything thru it and it functioned flawlessly with everything

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