M-4 barrel length

Discussion in 'Rifle Country' started by newbuckeye, Mar 3, 2014.

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  1. newbuckeye

    newbuckeye Member

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    I am thinking of getting an 11.5 inch upper, and am wondering how it will affect the range/accuracy compared to the 16 and 20". It's a 1-9 like the others, just shorter.
     
  2. rcmodel

    rcmodel Member in memoriam

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    I will not affect the accuracy.

    It will affect the velocity, to the tune of about 500 FPS less then a 20"
    Or 400 FPS less then a 16".

    That of course affects the flatter trajectory & higher energy of the longer barrels at long range.

    And you probably know, but a rifle barrel has to be 16" long to prevent it being classified as a SBR and need a $200 ATF tax stamp.

    You can permanently attach a long flash hider to the shorter barrel by welding or a blind pin that cannot be removed to make it 16".

    Myself?
    I'd rather have the velocity increase of the longer barrel to start with.
    Velocity is what makes the .223 work.

    rc
     
  3. Theohazard

    Theohazard Member

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    Barrel length doesn't directly affect accuracy, though a shorter sight radius can make it harder for the shooter to be as precise with iron sights. And a slower bullet is more affected by wind because of the lower velocity. This site shows how much lower your velocity will be.
     
  4. 1911 guy

    1911 guy Member

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    I agree with rcmodel. While the short ones look cool, they give up a lot of velocity, they require a 200 dollar tax stamp with an approximate six month wait and they often have function problems due to the extremely short dwell time. The fixes to correct these cost more money.
     
  5. eldon519

    eldon519 Member

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    Just cause you referenced the M4, they are usually 14.5" long with a 1-7 twist rate rather than 11.5" a 1-9.
     
  6. Onmilo

    Onmilo Member

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    XM177
    XM177E1 (With forward assist)
    Colt Commando carbine
    These are the 11.5" barrel weapons
    A SOCOM CDW (Close Defense Weapon) uses a 10.5" barrel.
    All M4 Carbines use 14.5" 1/7" twist barrels
    Having had an 11.5" Carbine and now owning a 14.5" M4 1/7" with permanent flash suppressor, (YHM Phantom, pinned and welded),
    my suggestion is go with a 14.5" upper.
    Less blast, more velocity, lots more practical accuracy.
     
  7. henschman

    henschman Member

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    Instead of the tax stamp, you could put a pistol buffer and SB-15 "arm brace" on it. It works just like a stock, but keeps the gun legally a pistol.
     
  8. Arizona_Mike

    Arizona_Mike Member

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    A few months ago some folks on this and other forms were freaking out about about me using an SB15 while waiting for a stamp. Last night at USA Auto Weapons in Scottsdale I saw a whole rack of these "pistols" for sale to the general public. SIG is even selling them with an oversized pistol buffer tube to increase "length of pull" er . . . I mean arm length :)

    [​IMG]

    The SB15 appears to be becoming common. Large companies are selling their "NFA hacks" as eagerly as small companies were in the last few years.

    Mike
     
  9. Theohazard

    Theohazard Member

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    Yeah, the SB15 is somewhat revolutionary when it comes to the whole AR pistol vs. SBR conundrum. And before someone comes on here and says it's illegal to shoot from the shoulder (it seems to happen any time the SB15 is mentioned on the internet): No, it's perfectly legal to shoulder it and shoot it like a rifle. The BATFE cannot restrict how you shoot a firearm, only how that firearm is designed. And they've officially determined that the SB15 is an arm brace that doesn't change a firearm's designation as a pistol. Think about it: A pistol is defined by the BATFE as being designed to be fired with one hand only; if it was illegal to shoulder the SB15 then it would also be illegal to shoot any handgun with a two-handed grip.
     
  10. FrankCastleThePunisher

    FrankCastleThePunisher Member

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    The Sig M400 AR pistol comes comes with a 11.5" barrel and 1x7 twist rate and the SB15 brace for about 28" OAL, and without having to buy the stamp.
     
  11. MistWolf

    MistWolf Member

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    11.5" upper: Yes
    1/9 twist: No, unless you want to be limited to shorter length bullets like the 55 grainers normally are. Because of the velocity loss from a barrel this short, RPMs will be lower making longer bullets less stable or even unstable

    An 11.5 inch rifle is very handy and will make hits out to 300 yards easily. It's also a good length if you want to suppress it. The better makers like BCM put out very reliable rifles in this length. If I had the money, I'd be rockin' a suppressed 10.5 carbine. SBRs are a blast to shoot (pun intended)
     
  12. DoubleTapDrew

    DoubleTapDrew Member

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    I dunno that looks pretty cool but the BATFE also OK'ed the akins accelerator before they changed their mind and left a lot of folks with $1,000 non functioning 10/22 stocks
     
  13. MachIVshooter
    • Contributing Member

    MachIVshooter Contributing Member

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    12-15 right now, actually

    Not if they're done right. My 7.5 and 12.5 are every bit as reliable as my 16 inchers.
     
  14. RP88

    RP88 Member

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    why not look into a 14.5" barrel with a permanently attached flash hider?

    Less hassle that way, while keeping good velocity and still tad more compact. than the 16-inchers
     
  15. Arizona_Mike

    Arizona_Mike Member

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    If you are worried about the wait time either:

    1. Get a trust, sign up for e-forms, and get your e-form approved in about 90-95 days.
    2. Build it as a pistol with a virgin receiver and a SB-15 while waiting for a paper Form 1.

    My 10.5" 300BLK with pistol gas and an H2 buffer is also 100% reliable. In fact it would be a little overgassed if it were not for the Syrac.

    Mike
     
  16. wally

    wally Member

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    Another thing that always seems to come up in these "loophole" threads, but overlooks that the Akins Accelerator as approved was *not* the same as what they ended up delivering -- the added spring negated the approval and changed the classification.
     
  17. Theohazard

    Theohazard Member

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    Like Wally said, the Akins is different. And -- more importantly -- the SB15 is fairly cut-and-dried: THE BATFE has said it's designed as an arm brace for one-handed use. The only way they could justify changing their minds and banning it is if they determined that SIG was actually designing it to get around the SBR laws. But SIG is doing a great job of holding to the official "arm brace" line; there's zero evidence that it's intended to let you get around the SBR laws, even though we all know it is.

    Sure, I guess the BATFE could ban the SB15. But as long as they haven't banned much more scary things like the Slide-Fire stock, I highly doubt they'll worry too much about a rubber arm brace that just happens to work as a stock.
     
  18. mac66

    mac66 Member

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    I have a 11.5" bbl'd AR pistol with just a buffer tube. I don't have that arm brace thing, I just use the buffer tube to shoot from the shoulder. Works well and is accurate out to 2-300 hundred yards.
     
  19. newbuckeye

    newbuckeye Member

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    Thanks everybody! I am going to build a pistol lower for it, but I am also going to look for the 1/7. That wont be a deal breaker for me tho because most of what I shoot is already 55gr. I have some heavier stuff I use for yotes and such but not that much.
     
  20. meanmrmustard

    meanmrmustard Member

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    I agree with Mistwolf that SBRs/pistols of a working length (10.5"+) are not only handy, but fun.

    For those who say that the 5.56 needs that speed of a longer tube for effectiveness via velocity, I ask you this:

    Have you seen the ballistic gel impact footage/pics of the Mk 262 Mod 1 from an 11.5 barrel? That round in media with a MV of only 2300 fps looks like a grenade went off at the ten inch mark.

    Devastating.
     
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