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Centerfire Rifles - Semiautomatic or Gas Operated Centerfire rifles, carbines and other gas operated rifles.

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  #1  
Old 12-18-2013, 3:17 PM
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Default Pressure vs Barrel length study 5.56

http://sadefensejournal.com/wp/?p=1093
A little old but good info non the less

Here is a good little write up regarding the shortening of barrels and change of twist rates and the increased pressures and flash / noise increase.


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Measurements for barrel lengths of 24 down to 5 inches showed that the pressure in the barrel at the moment of uncorking varied from 4,800 psi for the 24-inch barrel to over 25,000 psi for the 5-inch barrel. This is represented in Graph 1 and summarized in Table 1. Plotting the logarithm of the uncorking pressure against the barrel length produces a relatively straight plot, indicating that the pressure rises exponentially with shortening of the barrel.


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Old 12-18-2013, 3:35 PM
Calplinker Calplinker is offline
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Good information there. Very interesting that the muzzle velocity actually increases when you shorten the barrel from 21" to 20". I'm always amazed that the velocities remain so high with such short barrels. An 11" barrel delivers a muzzle velocity of nearly 2700 fps.
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Old 12-18-2013, 5:42 PM
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Quote:
Originally Posted by Ninety View Post
...Here is a good little write up regarding the shortening of barrels and change of twist rates and the increased pressures...
Bore pressures go down as you get away from the chamber. No surprise there.

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Originally Posted by Calplinker View Post
...Very interesting that the muzzle velocity actually increases when you shorten the barrel from 21" to 20"....
Most likely an anomaly in the data, all centerfire cartridges keep gaining velocity as barrel length increases up until the barrel length is unusable. Rimfire is done at 16 inches but not centerfire.
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Old 12-20-2013, 10:45 AM
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Quote:
Originally Posted by Calplinker View Post
Very interesting that the muzzle velocity actually increases when you shorten the barrel from 21" to 20".

That's a big blip in the data at 21" as they are showing a 150fps dip by adding an inch of barrel length and then it starts gaining velocity again.
We actually call that BAD data.
That velocity change does not happen in reality...
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