Author Topic: 14.7", what is the significance?  (Read 3239 times)

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Offline RIPNBST

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14.7", what is the significance?
« on: December 16, 2014, 07:17:24 PM »
What is the significance of the barrel length selection by the US armed forces for the M4 at 14.7"?  Is that the length at which NATO rounds achieve full powder burn?  Does this combination of barrel length with the carbine gas system achieve "perfect harmony"?


Why not a 14" or even shorter barrel?  I know they'd be sacrificing velocity thus effective range going shorter but still, 14.7" is such a specific number there must be some science behind its selection.  I did a brief google search and came up empty.  Admittedly I didn't go to the end of the earth looking but curious if anyone on here with more AR platform knowledge would be willing to share with the class?
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Offline TXAZ

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Re: 14.7", what is the significance?
« Reply #1 on: December 16, 2014, 07:31:47 PM »
There could be some other factors as well:   Dr. Gerald Bull did research 30 years ago on the optimum length of a barrel (mainly large bore) and came up with various 'length rules' to optimize accuracy and precision and minimize harmonic vibration. 
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Offline Lrdplatypus

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Re: 14.7", what is the significance?
« Reply #2 on: December 16, 2014, 07:52:28 PM »
I read a very interesting study that indicated that shorter barrels are more accurate than longer barrels. Longer barrels give more velocity up to a certain point though.

As for your first question, 20 inches is the length at which the 5.56 cartridge burns all its powder.

I don't know why the m4 has a 14.5 inch barrel, probably just a good trade off between velocity, accuracy, and maneuverability.
« Last Edit: December 16, 2014, 11:42:09 PM by Lrdplatypus »
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Offline Shipwreck

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Re: 14.7", what is the significance?
« Reply #3 on: December 16, 2014, 07:59:03 PM »
I have read that 223/5.56 performance suffers if the barrel is too short. The round doesn't get up enough speed to perform as designed. There must be something to do with that and the barrel length