July 29th, 2021
.308 Win Velocity Vs. Barrel Height — 28? To 16.5 Cut-Down Test
One wonders if barrels have a greater velocity gain if they are longer. Rifleshooter.com conducted an interesting test to answer that question. They cut a.308 Win bar from 28? All the way down to 16.5′. The cuts were made with a rotary saw in one-inch intervals. The magnetospeed chronograph measured velocity at each length. The test was made even more interesting by the chronographing of four types of.308 Win factory ammunition at each length.
This test is very useful if you are thinking about building a hunting rifle with.308 Win cartridges, or if you want to make your F-TR rifle lighter in order to save weight.
READ RifleShooter.com. 308 Win Barrel Cut Down Test Article.
Test Barrel lost 22.7 FPS per inch (.308 Win Chambering). How much velocity did each 1 lose, on average? reduction in barrel length? This may surprise you. A barrel reduction of 28? The average speed loss for all four types of.308 ammunition was 261 fps. This is a loss of 22.7 fps/inch. This chart shows velocity variations for all four ammo types:
Summary of Findings
For all four types of ammo, the average velocity loss per inch was 22.7 FPS. The average FPS loss per inch by ammo type was 24.6 (Win147 FMJ), 22.8(IMI 150 FMJ), 20.9 (Fed GMM 162gr) and 22.5 (Win 180PP).
These numbers are in good agreement with the estimates in reloading manuals. Testers observed that the 308 Winchester’s muzzle velocity would increase (or decrease) by approximately 20% compared to a standard 24. barrel’.
How the Test Was Performed
According to the testers, their procedure was as follows: “Ballistic data were gathered using a Magnetospeed ballistic chronograph mounted on a barrel. The rifle was fired from a front rest equipped with rear bags and five rounds of each type ammunition at each barrel length. Each round was logged with the standard deviation and average velocity. We decided to stop collecting data on group sizes because we would be collecting data on 52 different ammunition combinations and barrel lengths. After data had been gathered for each cartridge at the given barrel length, the rifle could be cleared and the bolt removed. The barrel was removed using a cold saw. For the next length, the test protocol was repeated. The temperature was 47? F.”
Click HERE to read the Rifleshooter.com test. These charts include detailed charts with inch by inch velocity numbers, multiple line charts and complete data sets for every type of ammo. Rifleshooter.com offers ballistics graphs that show trajectories for different barrel lengths. RifleShooter.com did a thorough test.
You will get different results with 6mmBR and a longer barrel
Rifleshooter.com’s barrel cut-down test for.308 barrels is quite different from the results we obtained years ago using a barrel chambered to hold the 6mmBR cartridge. We were able to reduce the length of our 6mmBR barrel from 33? to 28? We lost 8 FPS per inch when we reduced our 6mmBR barrel from 33? to 28? This is obviously a different cartridge type. However, our 6mmBR barrel ended length was 5? Rifleshooter.com has a.308 Win start length. This is longer. With shorter barrel lengths and larger cartridges, velocity loss can be more severe. Powder burn rates can also play a role.
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Tags:.308 Win Barrrel, Bill Marr Gunter, Cut-Down Test. Rifleshooter.com. Velocity barrel length
