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Thread: 10.5" Or 11.5"??? I need help!

  1. #1
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    10.5" Or 11.5"??? I need help!

    I applied for my stamp, I still have a while to wait still but I need help deciding on an upper. What should I go with 10 or 11.5"? I know this is gonna be a personal preference thing, so I would like to hear from you guys, and all that have both. What route should I go. This is my 3rd build BUT, my first SBR. I appreciate it guys, Thank you
    Last edited by BCmJUnKie; 05-22-11 at 04:25.
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    Its personal preference, sorry. Some would argue the reliability bonus of just that 1" that the 11.5 has, but I dont believe it. Either will serve you well. FWIW, I run a BCM 11.5, and never had any issues at all, with a few thousand rounds. One of my training partners runs a LMT 10.5 upper, and the same results with over 5500 rounds the last time he told me. Its up to you.
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    Quote Originally Posted by bsmith_shoot View Post
    reliability bonus of just that 1" that the 11.5 has
    And that little extra velocity. There's a link on ARFtard in BCM's forum that explains why they don't offer barrels shorter than 11.5.
    "You people have too much time on your hands." - scottryan

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    I'm no expert, but to me it comes down to balance. Perceived reliability and velocity vs. length. If you buy from a reputable source, I don't see reliability being that much of an issue. There are lots of quality 10.5" guns running just fine.

    I built a 14.5 (pinned to 16) for vehicle ops to avoid the NFA route and make it as short as possible. After a couple of months, I found it too long to be comfortably maneuverable, so I've decided to go the NFA route anyway and do a 10.5". Most of the scenarios we've trained for or found ourselves in are limited to engagement in the 25M to 100M range. For MY purposes (and with my somewhat limited understanding of all the issues) the shorter barrel outweighs the 1" ballistic advantage of the 11.5". Once I get the 10.5" built, I will spend some serious range time finding the right ammo for it.

    Bottom line is: Consider the employment of the weapon - balance your needs, get a gun and shoot it.
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    Quote Originally Posted by markm View Post
    And that little extra velocity. There's a link on ARFtard in BCM's forum that explains why they don't offer barrels shorter than 11.5.
    I do agree with the added velocity, but I swear man, ive seen so dang many 10.5's run like a sewing machine, to say theyre not reliable. I understand the cyclic rate theories, and how the gas system works, but seeing all those little rifles run, IDK, kinda makes it hard for me to argue reliability is better from one to another.
    "Blessed be the Lord my strength, which teacheth my hands to war, and my fingers to fight."
    -Psalm 144:1
    "Our houses are protected by the good Lord, and a gun; you might need 'em both, if you show up here not welcome, son."
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    Quote Originally Posted by markm View Post
    And that little extra velocity. There's a link on ARFtard in BCM's forum that explains why they don't offer barrels shorter than 11.5.

    My $0.02

    If the extra velocity is needed out of another inch but you need an SBR, it's time to look at a bigger caliber.

    As was mentioned above if you buy from a reputable manufacturer there shouldn't be any reliability issues. Many select LE units are running 10.5" rifles with much success. We're referring to SBR's, which are not meant to be employed as long range weapons, however I have attended classes in the past where an individual with a 10.5 was getting excellent groups out at 200 which should be no surprise.

    I agree with Noveske's train of thought which can be found here, it's logical and it makes sense:

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  7. #7
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    40% improvement in dwell time with the jump from 10.5" to 11.5" It is really a personal choice these days. My first was an LMT 10.5" second was a BCM 11.5" Third is an upper with a BCM 11.5" bbl so I've chosen the 11.5" but I'm not getting rid of my 10.5".

    11.5"



    11.5" & 10.5"



    https://www.m4carbine.net/showthread.php?t=29132

    https://www.m4carbine.net/showthread.php?t=66980

    You also have the 10.3" and 12.5" to throw in the mix

    https://www.m4carbine.net/showthread.php?t=54320

    Paul from BCM posted this here and on m4c:

    Q: Why BCM chose the 11.5" SBR over the 10.5"

    I get this question a lot. It is a good one. When we spec our program we can build anything we would like, so we sat down and looked at the pros and cons.

    First Statement: I know a good 10.5" SBR can run very well. I personally own a semi MK18 type and it runs great. No problems.

    A: Dwell time.
    Dwell time is the time that your gas operated weapon maintains pressure to continue the cycling of the weapon. It primarily exsists from the time the bullet passes the gas port in the barrel to the time the bullet exits the muzzle. When you pull the trigger and fire the weapon the movement of the bolt carrier group unlocks the bolt, extracts, and ejects the spent casing. Then it cocks the weapon, feeds, chambers the next round, and then locks again. One of the thing that can make SBRs finicky is the dwell time (or lack of).

    The 11.5" carbine is approximately 4% longer weapon than its' 10.5" counterpart, but this extra inch gives the barrel a 40% increase in length for dwell time. IMHO, this is an excellent trade off. This additional dwell time (all other things being equal) will allow the carbine to be more forgiving to different ammo types, extremes in air temperature, weak or worn extractor springs, worn extractors, buffer weights, etc.

    Last Statement: For those folks who have a 10.5" that works very well, I would reply; me too. (see first statement)

    If I had to "go to war" with a AR15 Carbine, I would grab the BCM 11.5".
    The BCM 11.5" Runs Like a Dream.

    Hope this info helps,
    Paul

    The question comes up enough that a Sticky of Paul's answer might be helpful.
    "Real men have always needed to know what time it is so they are at the airfield on time, pumping rounds into savages at the right time, etc. Being able to see such in the dark while light weights were comfy in bed without using a light required luminous material." -Originally Posted by ramairthree

  8. #8
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    I like the extra comfort of that extra inch. Plus, I think Paul explained it pretty nicely.



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  9. #9
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    agreed with Iraqgunz. The extra dwell time is just added comfort knowing my weapon is always going to fire.....

    That said, I have a 10.5in Bushmaster upper(blah blah, first SBR before I knew any better). I had to open the Gas Port out to .072, and use an H buffer. I use a BCM BCG in it to eliminate any extra issues.

    But my main go to gun is a 12.5 BCM upper. IMO 12.5 is the perfect length between a "CQB" upper and a 400+ yard carbine.

  10. #10
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    I have a 10.5 and a 11.5, no question across a wide spectrum of ammo the 11.5 is more reliable.

    Personally I think the question should be 11.5 or 12.5?



    Good luck

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