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Thread: 11.5" BCM Short stroking

  1. #11
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    double Tap
    Last edited by matemike; 10-10-19 at 12:50.
    “Twenty years from now you will be more disappointed by the things you didn’t do than by the ones you did do. So throw off the bowlines, sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.”
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  2. #12
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    I'm very surprised that your rifle sounds under gassed, as your set up technically should be over gassed.

    The BCM barrel does not have a small gas port in the least.
    The M4-2000 to my knowledge has a lot of back pressure.
    An H buffer for that can and barrel seems too light.

    I'd look for a gas leak, gas key or a worn gas tube bulb, maybe a leaky gas block fit?

    I have an 11.5"BCM barrel, Surefire Socom RC2, LMT enhanced carrier and H2 buffer. It cycles everything and then some. I'd prefer a .69 or smaller gas port, I believe the BCM is at least .73 but may be as big as .76

  3. #13
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    Quote Originally Posted by TMS951 View Post
    I'm very surprised that your rifle sounds under gassed, as your set up technically should be over gassed.

    The BCM barrel does not have a small gas port in the least.
    The M4-2000 to my knowledge has a lot of back pressure.
    An H buffer for that can and barrel seems too light.

    I'd look for a gas leak, gas key or a worn gas tube bulb, maybe a leaky gas block fit?
    Gas block has no leak markings. Gas key is tight and air checked, not leaking.

    Perhaps it cycled that batch of V max’s too fast. If anything it was over lubed. Definitely not dry.
    “Twenty years from now you will be more disappointed by the things you didn’t do than by the ones you did do. So throw off the bowlines, sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.”
    - Mark Twain

  4. #14
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    Quote Originally Posted by matemike View Post
    Gas block has no leak markings. Gas key is tight and air checked, not leaking.

    Perhaps it cycled that batch of V max’s too fast. If anything it was over lubed. Definitely not dry.
    A lot of the feeding issues sounds over gassed, but then you say it does not lock back. The not lock back would lead me to think its over gassed, unless its so overgassed its out running the follower on the mag and not locking back.

    Do you have an H2 or even H3 buffer you could try?

    Does it run the hornady ammo with out the can?

  5. #15
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    Do you have another BCG? I had the same issue with a BCM 11.5 upper and did hours of troubleshooting with Pat Rogers and a local gunsmith. There was nothing wrong with upper or lower, it turned out to be the BCG from BCM.

  6. #16
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    Quote Originally Posted by TMS951 View Post
    A lot of the feeding issues sounds over gassed, but then you say it does not lock back. The not lock back would lead me to think its over gassed, unless its so overgassed its out running the follower on the mag and not locking back.

    Do you have an H2 or even H3 buffer you could try?

    Does it run the hornady ammo with out the can?
    Did you mean undergassed there?
    No H2 or H3 buffer.
    I'll try the V-max stuff without the can next. As far as this weekend, I'll just use the M855 surpressed for hogs as I know that has worked flawlessly for the life of this rifle.

    Quote Originally Posted by themonk View Post
    Do you have another BCG? I had the same issue with a BCM 11.5 upper and did hours of troubleshooting with Pat Rogers and a local gunsmith. There was nothing wrong with upper or lower, it turned out to be the BCG from BCM.
    I have an unused LMT enhanced BCG in my spare parts. But I need to try the M855 ammo and try the V-max unsuppressed first before I start swapping everything around. Come to think of it, the ammo is the only change I made this time to the range. I'll start with that first. Back to what I know works.

    I really hope and don't think my BCM BCG has a problem. Not after only ~2500 rounds, especially since I can't see or detect any defects. But hey, I'll take note of your experience with Pat himself. Thanks.

    I all reality, I just wanted to go to the range yesterday and check zero on some hunting rounds. Didn't expect to run into issues like this. The next range trip is going to be diagnosis and fixing. Once I can focus on that I'll have a lot to investigate thanks to everyone's suggestions.
    Last edited by matemike; 10-10-19 at 17:10.
    “Twenty years from now you will be more disappointed by the things you didn’t do than by the ones you did do. So throw off the bowlines, sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.”
    - Mark Twain

  7. #17
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    I must of missed where you said it does or doesn't pass the lock back test. If this passes a few times, you can eliminate short stroking as a failure mode.

    So, IMO, shooting 5.56 out of a short barrel with a can should probably have a H3 buffer or an AGB with H1.

    How's your extractor and spring holding up? Got a spare you can try when you go to the range?

  8. #18
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    By hand the bolt locks back every time, even when trying to do it as fast as possible. So I know the follower and bolt catch are good.

    With the V-max, it locked back 50% of the time. 40% it did not lock back, 10% of the time the last round jammed between the bolt face and feed ramps so I did not get a chance to fire the last round.
    Last edited by matemike; 10-10-19 at 19:10.
    “Twenty years from now you will be more disappointed by the things you didn’t do than by the ones you did do. So throw off the bowlines, sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.”
    - Mark Twain

  9. #19
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    Quote Originally Posted by matemike View Post
    By hand the bolt locks back every time, even when trying to do it as fast as possible. So I know the follower and bolt catch are good.

    With the V-max, it locked back 50% of the time. 40% it did not lock back, 10% of the time the last round jammed between the bolt face and feed ramps so I did not get a chance to fire the last round.

    Sounding more and more over-gassed IMO, maybe even some weak extraction?
    I would shoot it without the silencer, and if you still have issues, swap the bolt/bcg - again no silencer and see what happens.

  10. #20
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    Lol I won’t change the title to 11.5” BCM Overgassed just yet. Just need to sort this out next chance I have time at the range. I’ll even bring my chrono to check the speeds of this v-max batch. They might be hyper...?

    Gotta get on the road in the morning and be hunting all weekend.
    “Twenty years from now you will be more disappointed by the things you didn’t do than by the ones you did do. So throw off the bowlines, sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.”
    - Mark Twain

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