May 7th, 2019

6mm Creedmoor — How Many FPS Will a Shorter Barrel Cost You?

6mm 6.5 Creedmoor rifleshooter.com Bill Barr barrel length cut-down velocity test chronograph Magnetospeed chrono

Our friend Bill Marr of Rifleshooter.com has done it again — conducted a fascinating 6mm Creedmoor barrel cut-down test that reveals how velocity changes with barrel length. This time Bill started with a 24″ Proof Research stainless steel barrel on a Howa action. Bill says this was a well-used barrel, with over 1800 rounds through it. So, the velocities might be a bit different than a new barrel of similar length. Bill cut the barrel down in one-inch increments. Here are some results from the test:

24″ Velocity: 2893 FPS | 20″ Velocity: 2755 FPS | 16.1″ Velocity: 2598 FPS

CLICK HERE for FULL TEST REPORT on RifleShooter.com »

6mm 6.5 Creedmoor rifleshooter.com Bill Barr barrel length cut-down velocity test chronograph Magnetospeed chrono

6mm 6.5 Creedmoor rifleshooter.com Bill Barr barrel length cut-down velocity test chronograph Magnetospeed chronoFor this latest test, Rifleshooter cut the barrel in one-inch increments from 24″ to 16.1″ (just over legal minimum). Velocities were measured with a MagnetoSpeed V3 chronograph mounted on arm attached to the stock. This allowed the chrono to be adjusted inwards as the barrel was cut shorter, inch by inch.

For the 6mm Creedmoor cartridge, Bill loaded Hornady 108gr ELD Match bullets over 41.5 grains of Hodgdon H4350 with CCI 200 primers in new Starline brass.

The results were interesting to say the least. Bill reports: “Muzzle velocities ranged from 2,893 ft/sec at 24″ to 2,598 ft/sec at 16″ for a decrease in muzzle velocity of 295 ft/sec. Muzzle velocity changes per inch of barrel length ranged from 6 ft/sec per inch between 20 and 19 inches to 63 ft/sec per inch between 19 and 18 inches. Average velocity change per inch of barrel length was 37.9 ft/sec.”

Bill concludes: “An average drop of 37.9 ft/sec/inch of barrel is fairly significant and is what would be expected with a fast moving 6mm cartridge like the 6mm Creedmoor. While I’m used to seeing 6mm Creedmoors with slightly longer barrel lengths than 24″, when coupled with a sound suppressor the additional length can make moving the rifle quickly more difficult.

I’d suggest staying with longer barrel lengths wherever possible with this cartridge. At shorter lengths, it does give up more performance than its big brother the 6.5 Creedmoor.”

More 6mm Creedmoor Velocity Data from 2017 Cut-Down Test

If you’re curious about 6mm Creedmoor velocities at longer barrel lengths, back in 2017 Rifleshooter completed a 6mm Creedmoor barrel cut-down test from 31 inches all the way down to 17 inches. The test included four bullet types from 95 grains to 110 grains. With the 110gr Sierra MK, velocity at 31″ was an impressive 3110 fps. Surprisingly the velocity didn’t decrease that much for the first few inches. Even at 26″ (a five-inch reduction), measured velocity with the 110s was 3073 fps, a loss of 7.4 fps per inch on average. With a barrel shortened all the way to 20″ however, velocity had dropped down to 2949 fps, a significant (161 fps) loss. CLICK HERE for complete results from that 31″-17″ Barrel Cut-Down Test.

6mm 6.5 Creedmoor rifleshooter.com Bill Barr barrel length cut-down velocity test chronograph Magnetospeed chrono

CLICK HERE for 31″ to 17″ 6mm Creedmoor Barrel Test Report »

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January 21st, 2019

RifleShooter.com .308 Win Barrel Cut-Down Velocity Test

rifleshooter.com barrel .308 win cut-down test saw ammo GMM velocity magnetospeed

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.

rifleshooter.com barrel .308 win cut-down test saw ammo GMM velocity magnetospeed

READ RifleShooter.com .308 Win Barrel Cut-Down Test Article.

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:

rifleshooter.com barrel .308 win cut-down test saw ammo GMM velocity magnetospeed

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.”

rifleshooter.com barrel .308 win cut-down test saw ammo GMM velocity magnetospeed

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.

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