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Thread: Short stroking caused by BCG

  1. #41
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    Charles and Boyle calculated "gas laws" based on pressure, temperature, tube size, tube length and so on. There are lots of other gas laws engineers use to calculate the correct size for gas blocks. To add to all the other variables, now we have guys wanting seven inch barrels, Engineers do this for popular lengths of ARs. They have done the thinking and calculating. Re-engineering a machine is going to cause problems or may cause problems everywhere. Successful seat-of-the-pants engineering usually happens when the product is poorly engineered to start with. Like a Chevy for instance. People hot rod Chevys because they were crap to start with. Try that with a Mercedes and there will be tons of problems.

    Gas Laws
    https://en.wikipedia.org/wiki/Gas_laws

    Every time one of these engineering companies comes along with non-mil spec parts which they claim are better than mil spec and you start stacking these in an AR, how can there not be problems??????? Explain it to me again.

  2. #42
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    On how much leakage is tolerable:

    The graph below is an experiment in which the leakage area increased and the pressure in the carrier cavity (cylinder) was measured. Line (1) is confusingly listed as zero (0) leakage, when it is actually the system in nominal condition, which for reference, is an equivalent leakage area of about 0.700 mm^2, that includes the barrel-front sight, front sight-gas tube, gas tube-carrier key, carrier key-carrier, and carrier-bolt interfaces. The other lines, (2), (3) and (4) are the cavity pressure with the listed leakage area. The leakage area was controlled by increasing the clearance between the gas tube and carrier key. Under normal conditions, the gas tube-carrier key interface accounts for about 80% of the total leakage.



    (2) is about 2X normal leakage
    (3) 3X
    (4) 5X

    The resultant bolt/bolt carrier velocities are:
    (1) 63.32 fps (100%)
    (2) 49.97 fps (79%)
    (3) 44.29 fps (70%)
    (4) 37.73 fps (60%)

    This graph is based on a standard M16A1 rifle length gas system, for a carbine length the cavity pressures will be about 10% higher.
    Last edited by lysander; 12-30-20 at 19:15.

  3. #43
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    Quote Originally Posted by lysander View Post
    On how much leakage is tolerable:

    The graph below is an experiment in which the leakage area increased and the pressure in the carrier cavity (cylinder) was measured. Line (1) is confusingly listed as zero (0) leakage, when it is actually the system in nominal condition, which for reference, is an equivalent leakage area of about 0.700 mm^2, that includes the barrel-front sight, front sight-gas tube, gas tube-carrier key, carrier key-carrier, and carrier-bolt interfaces. The other lines, (2), (3) and (4) are the cavity pressure with the listed leakage area. The leakage area was controlled by increasing the clearance between the gas tube and carrier key. Under normal conditions, the gas tube-carrier key interface accounts for about 80% of the total leakage.



    (2) is about 2X normal leakage
    (3) 3X
    (4) 5X

    The resultant bolt/bolt carrier velocities are:
    (1) 63.32 fps (100%)
    (2) 49.97 fps (79%)
    (3) 44.29 fps (70%)
    (4) 37.73 fps (60%)

    This graph is based on a standard M16A1 rifle length gas system, for a carbine length the cavity pressures will be about 10% higher.
    Wow! That is an excellent start point to diagnose gas issues. Thanks for this!
    GET IN YOUR BUBBLE!

  4. #44
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    Quote Originally Posted by lysander View Post
    On how much leakage is tolerable:

    The graph below is an experiment in which the leakage area increased and the pressure in the carrier cavity (cylinder) was measured. Line (1) is confusingly listed as zero (0) leakage, when it is actually the system in nominal condition, which for reference, is an equivalent leakage area of about 0.700 mm^2, that includes the barrel-front sight, front sight-gas tube, gas tube-carrier key, carrier key-carrier, and carrier-bolt interfaces. The other lines, (2), (3) and (4) are the cavity pressure with the listed leakage area. The leakage area was controlled by increasing the clearance between the gas tube and carrier key. Under normal conditions, the gas tube-carrier key interface accounts for about 80% of the total leakage.



    (2) is about 2X normal leakage
    (3) 3X
    (4) 5X

    The resultant bolt/bolt carrier velocities are:
    (1) 63.32 fps (100%)
    (2) 49.97 fps (79%)
    (3) 44.29 fps (70%)
    (4) 37.73 fps (60%)

    This graph is based on a standard M16A1 rifle length gas system, for a carbine length the cavity pressures will be about 10% higher.
    How is the pressure expressed in this graphic?
    The number of folks on my Full Of Shit list grows everyday

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  5. #45
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    Quote Originally Posted by MistWolf View Post
    How is the pressure expressed in this graphic?
    Based on the label on the vertical axis, Mega Newton per square meter, or mega Pascal.


    Sent from my iPad using Tapatalk

  6. #46
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    Quote Originally Posted by Clint View Post
    For anyone who needs an upgrade, we have a few of these in stock now.

    Can you be more transparent with who manufactures your BCG?
    Its well known that BCM, SOLGW, etc use Microbest so I don't think its a NDA matter.
    You won't outvote the corruption.
    Sic Semper Tyrannis

  7. #47
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    Quote Originally Posted by MistWolf View Post
    How is the pressure expressed in this graphic?
    For those who prefer to think in American Standard Units:


  8. #48
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    Quote Originally Posted by lysander View Post
    The resultant bolt/bolt carrier velocities are:
    (1) 63.32 fps (100%)....
    Not crucial to the discussion here, but I think the cited carrier velocities are much too high — do they agree with other sources you might have? I found an old report on DTIC that claims something like 17 fps. Also, a speed of 63 fps for a mass of 1 pound (BCG + buffer) would imply a kinetic energy of 60+ ft-lb, far more than the 10 ft-lb of work you could get from a piston supplying 400 lb over a stroke of 0.3 in. Unit conversion error?

  9. #49
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    I may have read to wrong column in the data, or converted wrong.

    1) 9.2 m/s (100%)
    2) 7.9 m/s (85%)
    3) 7.3 m/s (79%)
    4) 6.3 m/s (69%)

    At least I wasn't shooting a spaceship to Mars or anything like that.

  10. #50
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    We wouldn't source from them if they weren't the BEST.

    Quote Originally Posted by prepare View Post
    Can you be more transparent with who manufactures your BCG?
    Its well known that BCM, SOLGW, etc use Microbest so I don't think its a NDA matter.
    Black River Tactical
    BRT OPTIMUM Hammer Forged Chrome Lined Barrels - 11.5", 12.5", 14.5", 16"
    BRT EZTUNE Preset Gas Tubes - PISTOL, CAR, MID, RIFLE
    BRT Bolt Carrier Groups M4A1, M16 CHROME
    BRT Covert Comps 5.56, 6X, 7.62

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