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Thread: Diagnosis check...bolt speed?

  1. #21
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    Diagnosis check...bolt speed?

    A friend of mine had these exact malfunctions on a PSA upper while running PMC bronze. We ruled out mags, lowers, BCG's, everything but the ammo.
    It would run on full pressured ammo just fine and even cheap Herters/Tula, but not PMC.

    He sent it back to PSA and they replaced the gas tube, even though we could find no excessive gas leakage and they polished the feed ramps a bit, but it still doesn't like the PMC. It will bolt override about 2 times per magazine.

    Strangely enough, the same lot of PMC will run in all 3 of mine. Two BCM middies AND a PSA middie.

    Kind of bizarre.
    Last edited by Pork Chop; 08-18-13 at 01:08.

  2. #22
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    Quote Originally Posted by Iraqgunz View Post
    Someone here pulled the FSB on a PSA carbine and it was around .093. My buddy locally grabbed a PSA upper out of curiosity and it was so overgassed it would run with an H3.
    If a 16 carbine has the correct gas port, what should you be able to run?? Just wondering.

    I was running some tests yesterday on my wifes PSA I put together for her ( lucky for me it has functioned flawlessly the couple years she has had it ).

    I was able to run a H2 with a Red spring, ran no problems, I didn't have a H3 to try. But she settled on a H /White spring combo that she said felt best.

    I have not meassure the port, so I don't know what it is.
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  3. #23
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    Quote Originally Posted by MK18Pilot View Post
    Given a serviceable magazine, the bolt group can't outrun it, period. This is one of those nagging errornet theories that just won't die.
    Add me to the believers list. Remember that the BCG puts downward pressure on top of the ammo stacked in the mag. If the BCG velocity is high enough, I believe the sudden downward pressure as the BCG moves rearward can push the ammo stack down into the mag enough to cause an air gap. Then the BCG/buffer bounce back off the RE and start forward before the mass of the ammo stack can reverse direction. Obviously the more ammo in the mag, the weight of said ammo and the particular amount of drag present all affect this. Someone with a transparent mag or Magpul window mag and a high speed camera could confirm or lay to rest this theory...

    Quote Originally Posted by Eric D. View Post
    FWIW My BCM 16" middy will run anything with an H3 buffer. It does have over 5k through it though.
    After reading a bunch of threads on here I decided to buy an H3 and take it with a standard carbine buffer to the range with some Tula to do a short stroke test:

    Both my BCM 18" SPR rifle gas and DD 16" middy, will run Tula on top of a Rifle lower or carbine with H3...

    FYI, brass (steel LOL) ejected straight to 15:00 and dropped about 2 feet away (pretty weak ejection, but 100% bolt lock back none the less)...
    Last edited by Mall_Ninja; 08-19-13 at 18:15.

  4. #24
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    It's my opinion that a 16 barrel with carbine or midlength gas system should be able to run with any buffer weight and a USGI spring using NATO pressure ammo. Using heavier buffers should mostly be for fine tuning. If a 16" gun with mid or CAR gas can't run with a heavier buffer I think it would be too close to the threshold of failure to consider reliable.

    Quote Originally Posted by 223to45 View Post
    If a 16 carbine has the correct gas port, what should you be able to run??
    Last edited by Eric D.; 08-19-13 at 18:45.
    B.A.S. Mechanical Engineering Technology

  5. #25
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    Quote Originally Posted by Eric D. View Post
    It's my opinion that a 16 barrel with carbine or midlength gas system should be able to run with any buffer weight and a USGI spring using NATO pressure ammo. Using heavier buffers should mostly be for fine tuning. If a 16" gun with mid or CAR gas can't run with a heavier buffer I think it would be too close to the threshold of failure to consider reliable.
    By "heavier buffer" do you mean H2, H3?

  6. #26
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    Correct.

    Quote Originally Posted by Tzed250 View Post
    By "heavier buffer" do you mean H2, H3?
    B.A.S. Mechanical Engineering Technology

  7. #27
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    My 16" carbine has run well with an H2 using NATO pressure ammo. Consistent ejection and always locks back. I'm going to shoot some 55gr. reloads next so I'll take my H buffer along in case the H2 is too much.

  8. #28
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    Quote Originally Posted by Mall_Ninja View Post
    Add me to the believers list. Remember that the BCG puts downward pressure on top of the ammo stacked in the mag. If the BCG velocity is high enough, I believe the sudden downward pressure as the BCG moves rearward can push the ammo stack down into the mag enough to cause an air gap. Then the BCG/buffer bounce back off the RE and start forward before the mass of the ammo stack can reverse direction. Obviously the more ammo in the mag, the weight of said ammo and the particular amount of drag present all affect this. Someone with a transparent mag or Magpul window mag and a high speed camera could confirm or lay to rest this theory...
    ..
    I thought the bcg at rest was already in its lowest position, and that as it travels to the rear and the skid clears the round stack the next round will actually move up a fraction of an inch, well in advance of the bcg as it returns to battery.
    Are you claiming the bcg pushes the rounds down when it travels to the rear?
    " If i cannot be a good example Lord, let me be a terrible warning"

  9. #29
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    Quote Originally Posted by Mall_Ninja View Post
    FYI, brass (steel LOL) ejected straight to 15:00 and dropped about 2 feet away (pretty weak ejection, but 100% bolt lock back none the less)...
    Is it a Stag left-handed model? 1500 would be over your left shoulder around the 7-8 o'clock position....or the brass circled 360 deg around you back to the 3 o'clock position! That's wild!!
    Maybe the latter and that's why it was only two feet away, but that would mean really strong ejection to create a whirlwind!

  10. #30
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    We tested a S&W M&P15 at the Sandy Springs, GA class I did and the carbine ran with 4 different types of ammo with an H3 buffer. We tested the carbine with all 4 buffers and the Vltor A5.

    100% functioning and cycling.

    Quote Originally Posted by Eric D. View Post
    It's my opinion that a 16 barrel with carbine or midlength gas system should be able to run with any buffer weight and a USGI spring using NATO pressure ammo. Using heavier buffers should mostly be for fine tuning. If a 16" gun with mid or CAR gas can't run with a heavier buffer I think it would be too close to the threshold of failure to consider reliable.



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