Saturday Movies: How Velocity Varies with Barrel Length

For most larger centerfire cartridges, increased barrel length augments muzzle velocity. That’s why you see F-Open rifles with 30″ and even 32″ barrels. But there is a limit — at some point, increased barrel length may not yield any additional velocity. And in the case of rimfire, too much barrel length can reduce MV. Today’s showcase explores how barrel length affects muzzle velocity, both in centerfire and rimfire rifles.

In the photo above you can see a test rifle fitted with what may currently be the longest barrel fitted to a conventional rifle. This was created by the team at MDT (Modular Driven Technologies) to test how velocity varies with barrel length.

You can see the results of testing with this one-of-a-kind rifle in the MDT video below, the first in our Saturday video showcase. This is followed with an MDT rimfire barrel length/velocity test, and additional tests for the .308 Winchester, 6.5 Creedmoor, and .223 Rem cartridge types.

World’s Longest Rifle Barrel Cut to Determine Velocity Change

This may be the most interesting velocity by barrel length test ever put on video. The MDT (Modular Driven Technologies) team started with a 69″-long barrel, chambered for .308 Winchester. The ammo was Federal Gold Medal match with 175gr Sierra HPBT Bullets (Video 3:30). This barrel had actually been fabricated from multiple sections, a challenge in itself.

Velocity was measured in one-inch increments starting at 69″ and going down to 19″. The speed at 69″ was 2778 FPS while the final speed, at 19″ barrel length, was 2567 FPS. “That is a difference of 211 FPS from the longest point to the shortest point”, observed MDT’s tester. Note that, the velocity did show fairly constant change per inch from 19″ to 45″. So going beyond 36″ inches can actually increase velocity. However, from 45″ to 61″ inches the velocity actually declined a bit. SEE VIDEO at 6:55 time-mark, and check out the chart below.

Ultra-Long .22 LR Rimfire Barrel Cut-Down Velocity Test

This video features Part 2 of MDT’s “Cutting the World’s Longest Rifle” test. This time the team shoots the diminutive .22 LR cartridge from an ultra-long barrel. The results may surprise you: “Get ready to have your assumptions shattered as the MDT team chopped a .22 LR rimfire barrel away inch by inch, recording velocities at each barrel length. In this test, the MDT team looked to determine the optimal length for a .22 LR barrel, from the standpoint of velocity. How long is too long? How short is too short? Does shorter always mean faster? Does longer always mean slower?”

In fact, MDT’s testers determined that, with standard rimfire ammunition, the velocity started to decline after 16″ length. That surprised some of the testers. So with the small .22 LR cartridge, more barrel length can actually reduce muzzle velocity from increased in-barrel friction.

6.5 Creedmoor Barrel Length Test (24″ to 16″)

For this video, testers for Western Powders took a standard test barrel chambered for 6.5 Creedmoor and cut it down one inch at a time. The velocity for five rounds at each length was then measured with a chronograph to determine velocity loss per inch of barrel reduction. Overall the recorded velocity loss from 24″ to 16″ was 197 FPS, almost exactly 25 FPS per inch of length. The velocity loss rate was fairly constant inch by inch, as you can see from the graph displayed at the 4:00-minute mark in the video.

.223 Rem (5.56×45) Velocity Tests (9 Guns, 7.5″ to 20″ Barrels)

In this video, the team from Classic Firearms tests a variety of firearms chambered for .223 Rem (5.56×45). This starts with an Springfield Saint Victor AR-type pistol with a very short 7.5″ barrel. This yielded a 2183 FPS average. Then the team tested eight more guns with increasingly long barrel lengths, adding barrel length with each gun in sequence. The test concluded with a Colt XM16E1 rig with 20″ barrel. That Colt AR averaged 3052 FPS. The guns used (and barrel lengths) are listed below.

The overall results are discussed at the 13:45 Time-Mark.

.308 Winchester — 16″ Barrel vs. 24″ Barrel Velocity

With the .308 Win cartridge, many hunters prefer a shorter barrel for lighter carry weight. In this video, Gavin Gear of UltimateReloader.com compares .308 Win velocities with a 16″ barrel and a 24″ barrel, shooting the same ammo. Gavin notes: “We asked for input on our .308 build. Overwhelmingly, you all wanted a 16″ barrel, so ‘Shorty’ was born! Looking to compare velocities, I brought out my match .308 Win with a 24″ barrel to compare the results with some Hodgdon data.” CLICK HERE to read full report on UltimateReloader.com.

RifleShooter.com Barrel Cut-Down Testing

Along with these videos, our friends at RifleShooter.com have conducted a number of barrel cut-down tests, starting with fairly long barrels. Velocities were measured with each inch reduction

Most of us own a .223 Rem rifle. Now, thanks to our friends at Rifleshooter.com we can assess exactly how velocity changes with barrel length for this popular cartridge.

Rifleshooter.com performed an interesting test, cutting the barrel of a .223 Rem rifle from 26″ 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 .223 Rem/5.56 ammo were chron’d at each barrel length. The Rifleshooter.com team that conducts these tests has a full-service gun shop, 782 Custom Gunworks — visit 782guns.com.

Test Barrel Lost 25.34 FPS Per Inch (.223 Rem Chambering)
How much velocity do you think was lost, on average, for each 1″ reduction in barrel length? The answer may surprise you. The average speed loss of the four types of .223/5.56 ammo, with a 9.5″ shortening of barrel length, was 240.75 fps total (from start to finish). That works out to an average loss of 25.34 fps per inch.

*There may have been an error. The 25″ velocity was higher at 3221 fps.

See inch-by-inch Barrel Cut-Down Velocity Data HERE »

Rifleshooter.com observed: “Cutting the barrel from 26″ to 16.5″ resulted in a velocity reduction of 214 ft/sec with the UMC 223 55-grain cartridge, 244 ft/sec with the Federal M-193 cartridge, 288 ft/sec with the Winchester M855 cartridge and 217 ft/sec with the Back Hills 223 68-grain match cartridge.”

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. 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 45.7° F.”

CLICK HERE to Read the Rifleshooter.com Test. This includes detailed charts with inch-by-inch velocity numbers.

See More Barrel Cut-Down Tests on Rifleshooter.com
Rifleshooter.com has performed barrel cut-down tests for many other calibers/chamberings including 6mm Creedmoor, .308 Winchester, and .338 Lapua Magnum. See these test results at Rifleshooter.com.