6mm Creedmoor — How Velocity Changes with Barrel Length « Daily Bulletin

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July 20th, 2023

6mm Creedmoor — How Velocity Changes with Barrel Length

A while back, our friend Bill Marr of Rifleshooter.com 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

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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