Interesting Article on Barrel Length/Velocity

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archie_james_c

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Here's an interesting write up by Charlie Sisk that he posted on the fire. While obviously theres variables, its a pretty neat experiment. I know one things for sure, I don't think I'll be losing sleep over my lowely 22" barreled 7mm RSAUM d:h:

http://24hourcampfire.com/ubbthreads/ubbthreads.php/topics/5828100/1
 
This is the reason I have always laughed at the "I would buy it but that .280 has a 22" barrel and you need 24" for....."
The quality of the bore can have far more effect on the velocity than 4" of barrel.

For the .308 and 30-06 class of cartridges, 22" makes too much sense.
 
Number look weird and you can't argue with physics

I think that the numbers are biased!
Basically a bullet is pushed by the expanding gas produced by the propellant.
This means that the critical issue is expansion ration.

Realistic velocity changes vs muzzle length
http://www.loadammo.com/Topics/October05.htm

Great examples of different 30 Cal cartridges
http://www.z-hat.com/Efficiency%20of%20the%20300%20Hawk.htm

This is the best link: powder selection vs case capacity
There a list of all current cartridges and their expansion ratio
http://kwk.us/powders.html

Cartridge ER Equiv effeciency barrel length 30-06 22.5" (18")
-------------------------------------------------------------
308 Win 3.02 18" (14.4")
30-06 3.72 22.5" (18")
338 WM 3.85 23.3" (18.5")
270 Win 4.54 27" (21.5")
300 WM 4.80 28" (22.5")
7 RM 5.33 32" (25.5")

Note that a short length 308 Win is great, a normal length 30-06 is great and normal length 338 Win Mag is great, a long length 270 Win and 300 Win are great and a needs a long barrel 7 RM!!!

If you think that an 18" 30-06 makes sense then the values between braces are the equivalent length.

Both of my favorite cartridges 243 Win and 270 Win are almost identical an need a 22" to 26"-27" barrel to shine.

Alex
 
I highly doubt Charlie freaking Sisk would fudge numbers to get biased results. Like we know there's many variables and the numbers can be manipulated, but from a rather redneck style experiment, the conclusions turned out pretty well.

Besides what numbers really make the .243 and .270 "shine"...is does 3100fps really screw your 500 yard dope up compared to 3250fps?
 
i found the 300 wing mag data hard to believe till i saw his load used . it isnt a max load.

article states he used medium loads, max loads would see the gap widen as there would be more powder left to burn in the longer tube.
 
Both 243 Win and 270 Win need a 23"-24" barrel and if you want to use a shorter 20"-21" barrel, you should simply go for a 7mm-08 instead of a 243 and a 30-06 instead of a 270 Win.
For big magnums, the conclusion is even simpler get a 23"-24" barrel 338 Win Mag instead of a 26"-27" barrel 300 Win Mag and if you want a 22"-23" barrel 7 Rem Mag, get a 270 Win instead!

If you want efficiency, you simply need a longer tube when you increase case capacity and should decrease case capacity if you want to use a shorter tube.

The "Magical" Short Magnums can do in a 24" barrel what older magnums do in a 26" barrel simply because of lower expansion ratio (because improved propellants allow smaller cases).

Alex
 
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