Velocity loss per inch of barrel - 308

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Ohno

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I was wondering if anyone has tested the difference in velocity loss between the most common barrel lengths available in 308 Target actions.
Using match ammo in the 150-175gr weights.

The most common lengths are:
20" - Tactical HB style
22" - Sporter weight
24" - Target/tactical (Savage Model 10 FCP)
26" - Varmint (Rem 700 VLS)
 
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go to http://ww w.tacticaloperations.com/ click on articles and read the Dec 2000 swat write up. it has everything you are looking for. I was surprised when i first read it.
 
During the development of the Tango 51, Tac Ops took a standard 26-inch barrel and cut it down to 18 inches in one-inch increments. Between 10 to 20 rounds were fired at each invrement. They found that a 20-inch barrel provides for a complete propellant burn and no velocity loss when using Federal Match 168-grain BTHP, a cartridge that has become something of a law enforcement standard. Going to an 18-inch barrel only resulted in a loss of 32 feet per second (fps).
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This is the bit from the article that I was looking for.

This has what I'd consider more "accurate" information on velocity as it relates to barrel length.
http://ww w.loadammo.com/Topics/October05.htm

At least it involves mathmatical formulas :)
 
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Ohno said:
Quote:
During the development of the Tango 51, Tac Ops took a standard 26-inch barrel and cut it down to 18 inches in one-inch increments. Between 10 to 20 rounds were fired at each invrement. They found that a 20-inch barrel provides for a complete propellant burn and no velocity loss when using Federal Match 168-grain BTHP, a cartridge that has become something of a law enforcement standard. Going to an 18-inch barrel only resulted in a loss of 32 feet per second (fps).
Click to expand...

This data I find hard to believe...
 
There was an article on accurate shooter.com a couple of year ago that corroborates the numbers. Ut was a surprisingly low number/inch, however it is a logarithmic amount.
 
guntech said:
This data I find hard to believe...
Click to expand...

Explain, please.


What I have always wondered about that article is how it all applies to factory actions and barrels. The article states a standard barrel was used... but what is standard? The standard barrel on a Tango 51 is listed as a "Tac Ops proprietary chrome-moly or stainless steel Krieger." This is far from a basic Rem or Savage barrel. Plus, having the chamber and action done by the Tac Ops crew is an added bonus.

I am not saying the article is wrong- far from it. I have read a lot of posts from Mike R. and he is a man of his word. I just don't know how far you can take that data and apply it to a basic factory guns. Premium components must make a difference!
 
I chronied a 150 gr 308 load and got this:

Primer: Winchester (hard primers)
Powder: IMR 4895 45gr (listed max is 45.5 gr)
Bullet: Speer Hot-Cor 150 gr
Brass: Federal

(2760fps - measured - M14; 2590 fps in 18.5" Rem 600 - measured-)

Results with 165 gr SST's were almost identical - 170 fps velocity loss for about 4" of barrel loss. These loads were fired on the same day and were all from the same batch of reloads, and so I consider it a valid test.

I, for one, do not believe you can chop 6" or more from a barrel and not have a noticeable loss of velocity; unless you started with a 36" barrel or something.

And guys who own and chrony Swedish Mausers can also confirm, as I can, that a short barrelled M38 will lose at least 300 fps as compared to a long barrelled M96.
 
guntech said:
This data I find hard to believe...
Click to expand...

it hard to believe, but I actually Saw one Of Edmonton Finest out at Genesee Several Month ago, shooting Sako TRG 22 that had been cut down to 20" re thread, and shooting Federal Gold match , and the last round I saw on the Chronograph was 2709fps, average around 30fps different, that what he said, upon Checking out the Target, I saw one hole not bigger than a 45cal size, that was 4 round.
 
Perhaps this is a case where the .308 can reliably burn nearly all of it's powder in a short barrel so by extension the longer barrel adds nothing significant to the velocity? I would be interested to see the results from a long action or large calibre mag to see if the drop would also be so insignificant...I suspect not so much.
 
That is a good question for PGW, since there 338lapua Timberwolf is only 26", I don't believe that extended the barrel any longer than 26" would have greatly improve in Velocity, same for 300winmag or 7mm remmag.
 
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