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Old September 1, 2009, 12:52 PM   #1
LuckyStrike
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Barrel Length/Muzzle Velocity

Hi guys, Ive got a question regarding barrel length and muzzle velocity.

Lets say that I have an 'ideal' load for my rifle which happens to be a 308 Remington 700 with a 24" 5R barrel in 1:11.25, the load I have puts the 175 SMK out at 2600 ft/sec. Now, if I gave my friend some of this ammo but he has a 26" 1:12 barrel, how will the velocity be affected? What if I was using these same rounds on a 20" bbl?

Is there some sort of general rule/formula regarding generally how much more FPS you will get for every extra inch or so of barrel? And how would twist affect the velocity on, say two 24" bbl's; one in 1:11.25 and one in 1:12 using the same load?


(I know that each gun will vary and this is a pretty broad question, but any info would be great)
Thanks!
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Old September 1, 2009, 12:56 PM   #2
Brian Pfleuger
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http://www.chuckhawks.com/rifle_barrel.htm

Scroll down to "Velocity loss (or Gain)", or better yet, read the whole thing. It's very informative.
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Old September 1, 2009, 03:17 PM   #3
oneounceload
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The old standard rule of thumb from way back when I started reloading was 50fps per inch. If you're going by published velocities and not actual as measured by an accurate chronograph, it's just a guessing game anyway.
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Old September 1, 2009, 03:40 PM   #4
Tom Matiska
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Nosler's #4 lists 308 data for 24" barrel in the rifle section and 14" Contender data in the pistol section. The 10" difference is 250 with some powders, over 400 for others. See if your pet powder is one of those listed.

Interesting thing about the Nosler data is the * (most accurate) varies greatly between the two sections.... velocity isn't the only thing some powders loose in a short barrel.
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Old September 1, 2009, 04:20 PM   #5
LuckyStrike
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Interesting read, peetzakilla. From the numbers posted in the article it seems that for bullets traveling in the 2500-3000 range there is about a 20 fps difference per inch in bbl's 20" through 24".

Those charts where pretty much exactly what I was looking for, thanks for sharing.
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Old September 1, 2009, 04:41 PM   #6
Brian Pfleuger
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Chuckhawks is a great site.
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Old September 3, 2009, 01:05 AM   #7
kiwi56
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Barrel length verses velocity

A friend at work bought a nice model 70 in 300 Winchester Magnum, Against my advice he decided to cut the barrel down from 26 inches to 20 inches. When we chonoed loads velocity was down to less than 30-06 velocities out of a 22 inch barrel but using a lot more powder. Some of the powder was obviously being burn't out side the barrel as the muzzle blast was horrendous. Accuracy also went from MOA to minute of dinner plate.

Last edited by kiwi56; September 3, 2009 at 04:01 PM.
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