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Thread: 11.5" BCM Short stroking

  1. #41
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    Quote Originally Posted by jackblack73 View Post
    It seems like you're reluctant to run the H2, although I'm not sure why. It's not the dirty threads. The bolt is running too fast with the VMax. Just run the H2. I run my 11.5" BCM with standard carbine spring and H2 and it runs all ammo fine, suppressed and unsuppressed. I consider it the standard and run an H2 in all my rifles.
    It may technically be possible that the threads, when clean, are allowing enough pressure loss that the weapon malfunctions then when they carbon seal. It sounds very nerdish and labbish and all, but I guess we can't 100% rule it out?

  2. #42
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    Spot on.

    I'm confident all of this would be resolved with a smaller gas port.

    Quote Originally Posted by jerrysimons View Post
    WS6 hit the nail on the head. You confirmed your gun is in fact OVERGASSED with that particular v-max .223 ammo when you took the M4-2000 off and it cycled. That ammo maybe a hot batch or just have a different pressure curve (is it superfromance?). The symptoms you initially described as well as the 1 o’clock ejection indicated excessive carrier speed.

    You didn’t mention what magazines you are using but short strokes don’t cause the bolt to slip off the cartridge rim and drag up the case jamming it into the extension. Excessive carrier velocity outrunning the mag spring causes this malfunction as well as failures to lock back because the bolt gets ahead of the bolt catch before the follower can present the bolt catch up to stop it. A bad magazine can also cause these symptoms in a gun cycling properly.

    The AAC M4-2000 is a can known for its high back pressure, BCM’s 11.5” barrels are like 0.076” gas-ports which is not lightly gassed. You are only using an H buffer. I think you were getting by with the other ammo but that v max pushed it over the edge for whatever reason. I bet you a heavier buffer H2 or H3 will solve the problem.
    Black River Tactical
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 11.5" CQB, 9" PDW
    BRT OPTIMUM-S Barrel - 11.5" CQB Suppressor Gas Drive
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  3. #43
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    For a point of reference- my bcm 11.5” runs unsilenced with an H2 and sprinco blue. I expected it to be undergassed, but not the case.

  4. #44
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    Thanks guys. I think I'm started in the right direction. With your help I was able to diagnose that this BCM was in fact running too fast and not too slow.

    The H2 is staying and I'll run the hell out of it next time I go blastin'.

    Turns out I absolutely love shooting steel knock down targets and hangers. This being a new to me range I am getting a whole new realm of drills to do. I even see game wardens there utilizing barrels and pallets in new ways as well as their own vehicles.

    Hopefully my focus on the gun running properly will subside and I can focus on myself again. I need to work on my back pocket mag grabs for sure. And I might look into a ambi mag release in case anyone has any recommendations there. Being a lefty, mag changes are the thing I most struggle with. I can work the bolt release, charging handle and safety with normal controls pretty well. It's just dropping and grabbing a new mag with my off hand that is not smooth. I used to be a lot smoother when I really slowed it down and gained speed throughout a class. But lately I just suck again. Haha that's another topic. Thanks gain folks.
    “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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  5. #45
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    Quote Originally Posted by matemike View Post
    Thanks guys. I think I'm started in the right direction. With your help I was able to diagnose that this BCM was in fact running too fast and not too slow.

    The H2 is staying and I'll run the hell out of it next time I go blastin'.

    Turns out I absolutely love shooting steel knock down targets and hangers. This being a new to me range I am getting a whole new realm of drills to do. I even see game wardens there utilizing barrels and pallets in new ways as well as their own vehicles.

    Hopefully my focus on the gun running properly will subside and I can focus on myself again. I need to work on my back pocket mag grabs for sure. And I might look into a ambi mag release in case anyone has any recommendations there. Being a lefty, mag changes are the thing I most struggle with. I can work the bolt release, charging handle and safety with normal controls pretty well. It's just dropping and grabbing a new mag with my off hand that is not smooth. I used to be a lot smoother when I really slowed it down and gained speed throughout a class. But lately I just suck again. Haha that's another topic. Thanks gain folks.
    Just train it. Don't go using AMBI stuff until you're G2G without it. Here is how I go about it, and I am sure that others will have likely much smoother/better tutorials (without the weapon cycling itself, it made it a bit trickier, lol!).

    Also, tagged for pix of height-over-bore failures with gamewarden hood.

    Last edited by WS6; 11-15-19 at 18:32.

  6. #46
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    For an ambi mag release I would be looking at Forward controls design EMR-A.

  7. #47
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    Quote Originally Posted by matemike View Post
    Turns out I absolutely love shooting steel knock down targets and hangers. This being a new to me range I am getting a whole new realm of drills to do. I even see game wardens there utilizing barrels and pallets in new ways as well as their own vehicles.
    Generally speaking you want to shoot ammo traveling under 3000FPs on metal. With centerfire rifles, a good rule of thumb is 100 yards. Here is a link to a steel target safety manual:

    https://shop.actiontarget.com/conten...fety-rules.asp

    Quote Originally Posted by matemike View Post
    And I might look into a ambi mag release in case anyone has any recommendations there.
    This is a thread on the subject which I started and many others contributed their thoughts to: https://www.m4carbine.net/showthread...azine-Releases


    Quote Originally Posted by matemike View Post
    Being a lefty, mag changes are the thing I most struggle with. I can work the bolt release, charging handle and safety with normal controls pretty well. It's just dropping and grabbing a new mag with my off hand that is not smooth.
    The lefty work-a-round is pretty simple. First, the rear pocket carry isn't ideal, but I've been there, done that.

    Start by grabbing an empty magazine with your SUPPORT hand in a beer can grip, it's the example on the left: https://gundigest.com/wp-content/upl...load-Fifth.jpg The beer can grip is generally used for reloads from the strong side of the belt, and, in your case, the rear pocket.

    Now, using that grip insert the magazine into the mag-well, but stop short of seating it (so you don't have to use the mag release - yet). Next take the magazine from the mag-well, still maintaining the beer can grip, and run your thumb up the seam on the back of the mag. Maintaining this grip, place the mag in your rear pocket. Pay attention to how you have to move your fingers to keep your thumb and fingers on the mag as you put the mag fully into your pocket. This is going to be the starting position for your mag grab.

    For me I come into the pocket with my fingers and thumb aligned as when giving a hand salute. My my fingers curl around the mag as my thumb goes to the rear seam on the mag, I remove the mag from the pocket and as I rotate it into the mag well the thumb curls down arond the 'back side of the mag - grip the mag tightly at this point because you are going to firmly push the magazine up into the mag well and pull down to ensure it is seated.

    Now, to remove the magazine from the rifle in a timely, high-speed manner: Put your thumb on the mag release and wrap the rest of your SU{{ORT hand around the front of the mag WELL. From that position, keeping your support hand in contact with the handguard/rail extend your support hand forward into a firing position. Figure out how to get around any VFG's, etc., because this is the path your support hand should follow after you push-pull the mag on the reload.

    Go back and forth several times, making sure your SUPPORT hand thumb is hitting the mag release as your wrap your SUPPORT hand around the front of the mag WELL, and you are not wasting any motion extending back out into firing position.

    Take two mags and practice dropping the mag from the rifle and reloading from the pocket. Remember - fast follows form.'

    So, after we push-pull the mag, if the rifle has locked back, it is a simple matter to come up the front of the mag-well and rotate the support hand to use the index finger to hit the bolt catch and then, with no wasted motion, extend back out into firing position.

    I learned these work arounds on duty rifles without ambi controls, they are now so ingrained that unless I tell myself 'use the ambi' I might as well not have them.

    Hope this helped.
    Last edited by 26 Inf; 11-16-19 at 13:36. Reason: replace release with WELL and added SUPPORT
    Patriotism means to stand by the country. It does not mean to stand by the President... - Theodore Roosevelt, Lincoln and Free Speech, Metropolitan Magazine, Volume 47, Number 6, May 1918.

    To announce that there must be no criticism of the President, or that we are to stand by the President, right or wrong, is not only unpatriotic and servile, but is morally treasonable to the American public. Sedition, a Free Press and Personal Rule, The Kansas City Star, May 1918

  8. #48
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    Excellent. I'll work on that drill. I have not tried swapping mags with my strong hand much. I always tried to use my right, support, hand since the mag release is on that side.

    What I recall from a few classes was that the instructor always liked how smooth I tried to be. Back when I mock raced sport bikes on a closed track we all applied "Slow is smooth, Smooth is fast", I'm sure I can apply that strong left hand wrap around mag swap with being smooth.
    “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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  9. #49
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    Another easy fix for the bolt speed problem is something like a Bootleg adjustable carrier. I have a 6.8 SPC that was having the same problem with an AAC can. The adjustable carrier fixed that .

  10. #50
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    Quote Originally Posted by matemike View Post
    Excellent. I'll work on that drill. I have not tried swapping mags with my strong hand much. I always tried to use my right, support, hand since the mag release is on that side.

    What I recall from a few classes was that the instructor always liked how smooth I tried to be. Back when I mock raced sport bikes on a closed track we all applied "Slow is smooth, Smooth is fast", I'm sure I can apply that strong left hand wrap around mag swap with being smooth.
    My bad, you are using the SUPPORT hand for all manipulations involving mag release, seating the mag and hitting bolt catch.

    I emphasized touch points on the rifle more than either of these videos, because I believe that is the way to ensure proper form as learning:

    https://www.youtube.com/watch?time_c...ature=emb_logo

    (This guy gets a pretty weak beer can grip and his pull to ensure the mag is seated was weak or non-existent. This isn't as big an issue with a bolt back reload, however, if the bolt is forward it becomes more important as you have to defeat the spring pressure of the loaded rounds in the magazine to fully seat the mag, This is why many folks still download their 30 rounders to 28 rounds - makes seating the mag easier.

    https://www.youtube.com/watch?time_c...ature=emb_logo (I use the beer can grip, LV doesn't really)
    Patriotism means to stand by the country. It does not mean to stand by the President... - Theodore Roosevelt, Lincoln and Free Speech, Metropolitan Magazine, Volume 47, Number 6, May 1918.

    To announce that there must be no criticism of the President, or that we are to stand by the President, right or wrong, is not only unpatriotic and servile, but is morally treasonable to the American public. Sedition, a Free Press and Personal Rule, The Kansas City Star, May 1918

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