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Thread: 11.5" BCM Short stroking

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  1. #1
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    11.5" BCM Short stroking

    11.5" BCM upper. Carbine length gas. BCM lower, H buffer. M4-2000 suppressor

    Hornady 55 gr V-max .223 are causing rifle to short stroke every now and then, sometimes even dragging the next round into the chamber and crushing it between bolt face and feed ramps. Bolt almost never held open on last round. I was checking out the V-max thinking it should be a better bullet for a hog hunt that I'm going on this weekend.

    I have +/- 2500 rounds of M855 through this rifle flawlessly; suppressed and unsuppressed. FWIW I had my 16" S&W with H buffer not short stroke the V-max once and always held bolt open on last round. I guess the 4.5" more dwell time helped. I could kick myself because I had a carbine buffer at the range with me. I could have tossed it in the BCM and checked if that would be my fix right then.

    Should I just stick with the M855 for shooting hogs, or swap to a carbine buffer and use the V-max? I want to just bring one rifle and the BCM is already set up for the suppressor. I won't have time to get to the range again before the trip. And once I'm there, it's not really a place to put a carbine through it's paces. It's a high fence deer ranch. Flinging brass all over the place and making noise will not be on the agenda.

    Is there anything else I'm missing to look into? All mags acted the same on the BCM and all mags worked perfect on the S&W. It's got to be the .223 55gr load short stroking the SBR.
    “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

  2. #2
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    Probably ought to just stick with a known quantity and make the best of it.


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  3. #3
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    I would not recommend V-Max for hogs.

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    Quote Originally Posted by taekwondopreacher View Post
    I would not recommend V-Max for hogs.
    1st this.
    2nd- your not going to have a good time clearing malfunctions all day.
    3rd- check for signs of gas leaks. That setup should not be short stroking bare, let alone with a supressor. Did you try it without the silencer on, or rechecked that m855 still works?
    Last edited by MegademiC; 10-10-19 at 05:16.

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    I'm going to lay odds that your bcg speed is accualy going too fast. Like mega medic said try it with out your supressor. One thing to ask is what is your ejection pattern, it not always indicative of what you rifle is doing but can help diagnose problems.

  6. #6
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    Had the same problem with mine. Do me a favor and swap out the bolt carrier and see if it happens again.

  7. #7
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    Quote Originally Posted by MegademiC View Post
    check for signs of gas leaks. That setup should not be short stroking bare, let alone with a supressor. Did you try it without the silencer on, or rechecked that m855 still works?
    No and no
    But I was thinking the same thing: this set up should not be short stroking. Gas key and gas tube are not loose. I’ll inspect the gas block for leak marks and apply a shot of air to gas key.

    Quote Originally Posted by farmhard View Post
    I'm going to lay odds that your bcg speed is accualy going too fast. Like mega medic said try it with out your supressor. One thing to ask is what is your ejection pattern, it not always indicative of what you rifle is doing but can help diagnose problems.
    1 O’clock and solid ejection.
    What are indicators that the bolt is going too fast? I mentioned that some rounds were being picked up by the bolt dragging across the top of them and wedging them between the bolt face and feed ramps. Some rounds were pinched so bad that they looked like there were sliced open down the case wall. Bolt too fast?
    “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

  8. #8
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    FWIW I started with a standard H buffer in my BCM 11.5 and the brass was ejecting erratically. Switched to an H2 buffer and it resolved the issue.
    Last edited by younggrasshopper; 10-25-19 at 18:39.

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    I had to install a reduced weight spring in mine to cycle 100%. There are a few makers of reduce weight springs and some are actually aimed at 300 bo specifically. I got mine from Gunsprings.com aka Wolff Springs. http://www.gunsprings.com/index.php?...D=1&dID=79#490 Item 16505 on that link.

  10. #10
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    Quote Originally Posted by patrick sweeney View Post
    If it works just fine with everything but the V-max, then don;t use it. If you want to dig in and discover why, go for it, but consider it R&D, not curing a problem. I've tested a metric buttload of firearms over the years, and now and then you just run into a case of "ammo hate." Known, reliable, facotry ammo that works jsut fine in a host of other firearms, for some reason the one being tested just hates. In cases like that, I just don't use that ammo.
    Great idea. It worked with everything suppressed and unsuppressed EXCEPT the V-max suppressed. All I may ever do is check those v-max velocities. See if it was a hot batch or something. Not gonna mod up my reliable gun to make one random round work.

    Quote Originally Posted by younggrasshopper View Post
    FWIW I started with a standard H buffer in my BCM 11.5 and the brass was ejecting erratically. Switched to an H2 buffer and it resolved the issue.
    I have since acquired a barrage of different buffer weights in case I ever run into a frustrating situation like that again. Still running the original H buffer though as it’s worked well thus far.
    “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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