Impact of Different Barrel Lengths on the 5.56x45 Round

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    Charlie Foxtrot
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    Impact of Different Barrel Lengths on the 5.56x45 Round

    Post by Charlie Foxtrot on Mon Feb 20, 2017 7:06 pm

    All y'alls shooting AR-15s probably wondered what the different barrel lengths do to the performance of the 5.56 round. This study seems to answer that question in well-reasoned, scientific manner.

    Barrel Length Studies in 5.56mm NATO Weapons

    Unsurprisingly (at least to me), a 20" barrel gives the best velocity. Those with a barrel length 10" or less are paying an significant performance price.  Another nod to 300 BLK.  

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    Tennessee Jed
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    Re: Impact of Different Barrel Lengths on the 5.56x45 Round

    Post by Tennessee Jed on Tue Feb 21, 2017 2:57 pm

    I've heard about this before. Very interesting. And that's just muzzle velocity. Once you get out to 100 yards or further, those 5.56 SBR's look even more worthless to me.

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    Devereaux
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    Re: Impact of Different Barrel Lengths on the 5.56x45 Round

    Post by Devereaux on Thu Feb 23, 2017 8:17 pm

    Well, if they are anything like Nam, 100 yd clean shot is a MESS. Hard to do that much tissue damage with any other. bullet. But then they probably made them ballistically stable.

    Too bad. You hit a gooner and you could tear off his arm. LOVE to see that in a riot. There would be all KINDS of complaining.
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    Re: Impact of Different Barrel Lengths on the 5.56x45 Round

    Post by Tennessee Jed on Thu Feb 23, 2017 8:21 pm

    Dev, someday, I hope you and I are in the same town so I can buy the whiskey in exchange for hearing some of your stories.
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    Re: Impact of Different Barrel Lengths on the 5.56x45 Round

    Post by Devereaux on Thu Feb 23, 2017 11:09 pm

    Well, we almost made it year ago. I did go visit CF - and a grand time we had, too.
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    Charlie Foxtrot
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    Re: Impact of Different Barrel Lengths on the 5.56x45 Round

    Post by Charlie Foxtrot on Thu Mar 02, 2017 9:14 pm

    Devereaux wrote:Well, we almost made it year ago. I did go visit CF - and a grand time we had, too.

    Got to do that again. With whisky.
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    Re: Impact of Different Barrel Lengths on the 5.56x45 Round

    Post by Charlie Foxtrot on Thu Mar 02, 2017 9:29 pm

    Devereaux wrote:Well, if they are anything like Nam, 100 yd clean shot is a MESS. Hard to do that much tissue damage with any other. bullet. But then they probably made them ballistically stable.

    Too bad. You hit a gooner and you could tear off his arm. LOVE to see that in a riot. There would be all KINDS of complaining.

    According to a buddy who spent time in the sandbox - there's no better antipersonnel round than the 55 gr (M193) bullet. From the Hajis he examined, the round had a distinct tendency to tumble inside a body, doing a tremendous amount of damage. If the round hit bone, there was better than even chance of the round breaking apart at the cantilever. Dev, was the 193 used in 'Nam?  

    The vaunted 62gr "Green Tips" (M855) would merely drill nice, polite, through and through holes.


    Last edited by Charlie Foxtrot on Thu Mar 02, 2017 9:52 pm; edited 1 time in total
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    Devereaux
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    Re: Impact of Different Barrel Lengths on the 5.56x45 Round

    Post by Devereaux on Thu Mar 02, 2017 9:39 pm

    Not sure just what we had. I would expect it was the 55-gr round, but it was complied a lot differently. For one thing, there was calcium in the powder to keep it "dry" and that mixed with the moisture in the barrels to RAPIDLY cause corrosion, nixing the barrel value. Wasn't until we got the chrome-lined barrels things were better, but those were slow in coming, at least in the Marine Corps. I had something like 39 men in my platoon and something like 32 of the rifles were gauged "unserviceable". But they only took about 6 of them at a time and swapped out barrels, leaving new guns. Then a week later, they did it again.
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    Re: Impact of Different Barrel Lengths on the 5.56x45 Round

    Post by Devereaux on Thu Mar 02, 2017 9:46 pm

    This of course brings up the fact that velocity does not necessarily predict terminal performance. Our rounds were DEVASTATING - but only if you got a clean shot. ANYTHING could make it tumble, so miss the mark. I had an M-14 in each squad for those occasions where you needed to make a straight shot at distance.
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    Re: Impact of Different Barrel Lengths on the 5.56x45 Round

    Post by Cornmastah on Tue Mar 07, 2017 10:27 am

    Yeah, those shorty 5.56 barrels really kill the cartridge's benefits of fast moving small projectiles. That's why I still don't have a shorty 5.56 upper, while I have 4 other calibers in 10-12" barreled uppers. 300 blk does excel in that area of short barrels.
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    Re: Impact of Different Barrel Lengths on the 5.56x45 Round

    Post by Devereaux on Wed Mar 08, 2017 11:59 am

    I think 300 BLK was designed for short barrels and suppressors, as a building-clearing load. Keeps the noise down, which especially reverberated in structures and allows auto-fire from a relatively short rifle size (including suppressor).

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