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Thread: 5.56X45 NATO.....Barrel Length pressure results with the XM-855 AMMO

  1. #1

    Default 5.56X45 NATO.....Barrel Length pressure results with the XM-855 AMMO

    I am not sure why this research article seems to get in my face this time of year, but it does. This is the third yearly reading, and each time I digest more and more.

    http://www.sadefensejournal.com/wp/?p=1093

    It attacked me today from the front page of Western Rifle Shooter.

  2. #2
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    Quote Originally Posted by AGL4now View Post
    I am not sure why this research article seems to get in my face this time of year, but it does. This is the third yearly reading, and each time I digest more and more.

    http://www.sadefensejournal.com/wp/?p=1093

    It attacked me today from the front page of Western Rifle Shooter.
    It is Stupidity elevated to a Art Form.

    All because shorter barrels seem desirable, Cultural Shifts" are sooooo, important, don'tcha know.

    BUT they only cause problems, and when they try to alleviate them, they cause even more problems.

    From the Article...... "There has been a cultural shift from the 20-inch barrel length in the AR-15/M16 weapon systems chambered for the 5.56◊45 NATO cartridge to progressively shorter barrels for the purpose of producing an increasingly more compact assault/entry weapon without resorting to a bull-pup design. Simple usage of these short-barreled weapons has shown the necessity for both sound and flash suppression, the intensity of which (in exceptionally short barrel lengths) approached the intensity of a flash-bang diversion device. This shift toward shorter barrels has resulted in the U.S. Army and Marine Corps adopting the 14.5-inch barreled M4 carbine with a re-design of the 5.56◊45 from the 55 grain SS-109 to the 63 grain M855 ammunition to optimize this barrel length. The differing bullet design also necessitated a change in the rifling twist rate from the original 1:12 inches to 1:7 inches.

    Law enforcement and some special operation units have continued this trend by using weapons fitted with 10.5-inch barrels, and there is some misguided law enforcement interest (in these authorís opinions) in the M16 type weapons using 7-inch barrels. Besides the horrendous flash and sound levels, these ultra short barreled weapons introduce significant ancillary issues, including weapon functioning and reliability as well as projectile stability and cartridge lethality."

    No surprise to me.

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    Yeah, it seems like there is always someone that just has to prove what most folks already know. A rifle cartridge makes a lot of noise and doesn't work very well in a 7" barrel. Who woulda thunk?

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    There was a lot of useful information for me in that test. Like where is "Peak" Velocity achieved, and the negative effect of drag beyond peak velocity.

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    This data is great if you are using the exact ammo they tested. Use a different powder or bullet and it all changes.

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    There is a place in the report stating the barrel was drilled with ports prior to firing, and another where it was fired, pressures taken, then shortened and new port drilled. That needs to be cleared up. I strongly question the slight jump, then dip, then increase in velocity around 20". It should be a smooth progression. Something went wrong there.

    It is intuitive that a shorter barrel will have a bigger bang and flash. At least someone took the time to measure the big bang.
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    I didn't read the article but based on the quote above it appears the author an many riders neglect to recognize the "proper" intent of the short barrels is to maintain overall length when adding a suppressor.


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    I'm not on Seal team 6 so i dont really need a SBR. A 16" ar is plenty short for me.

    As far as reliability goes, a shorter barreled rifle 12.5"-16" can be manufactured to be just as reliable as any 20". different length gas systems, different gas port diameters, buffer weight and buffer springs can all be re calibrated and balanced out for a short style barrel. So reliability is not an issue as long as a solid gun builder is designing the rifle and its components.

    As far as power is concerned, the 5.56 was designed to be going at such hi velocities that when it begins to tumble once it hits flesh the extremely high speeds it travels at overwhelm the structural integrity of the round, causing it to fragment. While it will very slightly from bullet to bullet, 2700 fps + is when you have guaranteed fragmentation. With a shorter barrel rifle the muzzle velocity is less, therefore the bullet will fall below the 2700+fps requirement at a closer range. While the bullet will still tumble, it will not fragment which is where the 5.56 gets the majority of it killing ability from.

    If you want to learn about the 5.56, and by learn i mean have any question you can think of answered, check out this link...
    http://www.ar15.com/ammo/
    http://www.ar15.com/ammo/project/term_velocity.html
    http://www.ar15.com/ammo/project/term_fragrange.html

    The first link in the main page for it. The Questions are all listed on the left hand side. There is a lot of information and if you don't learn something then you are a better man than me.
    The next two links are part of that page that are related to what i was saying above. Sources is what college people call those i think.

    But yes, as far as the hype about short barreled ARs is concerned, its a lot of gun-magizine non-sense. People what to have the nicest stuff without proper understand of how to even effectively shoot a mil spec m16a4 to its full ability. American materialistic non-sense. Learn to out-shoot the inferior AR before you worry about dropping 2000+ on your setup.

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