.308 Win Barrel Cut-Down Test: Velocity vs. Barrel Length
With barrels, one wonders “Can a little more length provide a meaningful velocity gain?” To answer that question, Rifleshooter.com performed an interesting test, cutting a .308 Win barrel from 28″ all the way down to 16.5″. The cuts were made in one-inch intervals with a rotary saw. At each cut length, velocity was measured with a Magnetospeed chronograph. To make the test even more interesting, four different types of .308 Win factory ammunition were chronographed at each barrel length.
Test Barrel Lost 22.7 FPS Per Inch (.308 Win Chambering)
How much velocity do you think was lost, on average, for each 1″ reduction in barrel length? The answer may surprise you. With a barrel reduction from 28″ to 16.5″, the average speed loss of the four types of .308 ammo was 261 fps total. That works out to an average loss of 22.7 fps per inch. This chart shows velocity changes for all four ammo varieties:
Summary of Findings: The average velocity loss per inch, for all four ammo types combined, was 22.7 FPS. By ammo type, the average loss per inch was: 24.6 (Win 147 FMJ), 22.8 (IMI 150 FMJ), 20.9 (Fed GMM 168gr), and 22.5 (Win 180PP).
Interestingly, these numbers jive pretty well with estimates found in reloading manuals. The testers observed: “The Berger Reloading manual says for the 308 Winchester, ‘muzzle velocity will increase (or decrease) by approximately 20 fps per inch from a standard 24″ barrel’.”
How the Test Was Done
The testers described their procedure as follows: “Ballistic data was gathered using a Magnetospeed barrel mounted ballistic chronograph. At each barrel length, the rifle was fired from a front rest with rear bags, with five rounds of each type of ammunition. Average velocity and standard deviation were logged for each round. Since we would be gathering data on 52 different barrel length and ammunition combinations and would not be crowning the barrel after each cut, we decided to eliminate gathering data on group sizes. Once data was gathered for each cartridge at a given barrel length, the rifle was cleared and the bolt was removed. The barrel was cut off using a cold saw. The test protocol was repeated for the next length. Temperature was 47° F.”
CLICK HERE to Read the Rifleshooter.com Test. This includes detailed charts with inch-by-inch velocity numbers, multiple line charts, and complete data sets for each type of ammo. Rifleshooter.com also offers ballistics graphs showing trajectories with different barrel lengths. All in all, this was a very thorough test by the folks at RifleShooter.com.
Much Different Results with 6mmBR and a Longer Barrel
The results from Rifleshooter.com’s .308 barrel cut-down test are quite different than the results we recorded some years ago with a barrel chambered for the 6mmBR cartridge. When we cut our 6mmBR barrel down from 33″ to 28″, we only lost about 8 FPS per inch. Obviously this is a different cartridge type, but also our 6mmBR barrel end length was 5″ longer than Rifleshooter.com’s .308 Win start length. Velocity loss can be more extreme with shorter barrel lengths (and bigger cartridges). Powder burn rates can also make a difference.
Similar Posts:
- .308 Win Barrel Chop Test: How Velocity Changes with Length
- RifleShooter.com .308 Win Barrel Cut-Down Velocity Test
- .308 Win Velocity vs. Barrel Length — 28″ to 16.5″ Cut-Down Test
- How .308 Win Velocity Changes with Barrel Cut from 28″ to 16.5″
- Surprising Results in .223 Rem Barrel Cut-Down Velocity Test
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Tags: .308 Win, 7.62x51 cut-down test, Barrel, Rifleshooter.com, Saw, Velocity
This is a great test and I would commend people to read the 300 Win Mag test where they did the same thing.
In the good old days of Precision Shooting magazine (how we miss you!), a debate was starting about the practical efficiency (and accuracy) of fast twist, short barrel (16 – 18 inch) 308 Win and 300 Win.
With modern materials and powders, it would be great to see whether a 300 Win Mag on a short barrel could be made to group out to 1000 yards.
Hi Richard,
Thanks for the kinds words about the 308 and 300 Win barrel length posts. We also have a 223 and 7 rem mag up there.
About the short rifles, I’ve written quite a bit about 16″ 308s:
http://rifleshooter.com/2015/02/the-16-inch-308-winchester-bolt-action-rifle/
We stopped at 500 yards, but I had some legit 2.5″ 500 yard 5 shot groups. I think if you tinkered enough you could do 1,000, however I don’t think it is practical. The short barrels gas out pretty quickly.
photo link: http://rifleshooter.com/wp-content/uploads/2015/01/custom-16.5-rem-700-308.jpg
Would be more interesting to see maybe 35″ barrel down to 28″ Have always heard that barrels quit increasing in velocity after 34″. Would be interesting to find out.
Above 28, 30″ the change is very slight.
I had a 34″ Border on my Palma rifle for a time. Velocity was about 10 FPS below that of my 30″ Border. SD’s and ES were superior from the longer barrel, as was the sight picture. This was with Varget powder.
Great test ! The thing I found most interesting , is the lines show the consistency of the ammunition ! The Federal shows a fairly straight line.
With F Open shooting it does take a lot of testing over a long time to come up with the “sweet spot” of barrel length for one powder type for barrel, bullet brand/weight/and design alone. As a “Wildcatter” it gets more so! After 15 years I’m still working it out. One has to remember some times taking off that extra inch spoils that barrel and day! Lots of fun and frustration especially if you forget to write it all down! He,he.
Does anyone have data on bullet drop vs barrel length?
Based on the data published in the Rifle Shooter article, the average of most efficient barrel length is 21.7 inches.
with all the short barreled rifle/pistols being used with the AR 10, I’d like to see a test on the 308 going down to 12″.