What's the difference between short & long airgun barrels?
by B.B. Pelletier
Yesterday I made a comment about a longer barrel being more efficient with air in a precharged airgun and that got me thinking. I have danced around this subject but today I'll tackle it head-on. What is the difference between a short and long barrel in an airgun?
Spring guns like shorter barrels
Gerald Cardew and his son, Mike, wrote in their book The Airgun from Trigger to Target about an experiment to determine the maximum length a spring-gun barrel should be. When they performed this experiment in the 1960s , the low-powered .22 rifle they tested got its maximum velocity by the sixth inch of barrel. After that, the pellet was coasting. After 25 inches of barrel, the pellet began to slow from friction.
Today's spring guns are more efficient, and the barrel length required for maximum acceleration is closer to 10 to 12 inches. Caliber makes a difference, as well, but it's not that big a difference. So, spring guns favor shorter barrels over longer ones. Accuracy is not affected by barrel length as I pointed out in the posting on May 26, Are longer barrels more accurate?
CO2 & pneumatic guns like longer barrels
No conclusive tests have been run on this, to my knowledge, but I can easily prove that gas guns like longer barrels. An AirForce Talon SS shoots a .22 caliber Crosman Premier pellet at 830 to 850 f.p.s. when set to its highest power seting. Exchange the standard 12-inch SS barrel for an 18-inch optional barrel, and the top speed will be 925 to 940 f.p.s. with the same pellet. Exchange that for the 24-inch optional barrel and the top velocity climbs up to 1,000 f.p.s. with the same pellet. These results all use the same base gun and air tank, so the only thing that changes is the barrel length.
Notice that the top velocity doesn't increase as much going from the 18-inch barrel to the 24-inch barrel as it does going from the 12-inch to the 18-inch. That's because the additional six inches of barrel after 18 inches don't add as much as they do after only 12 inches.
The proof of greater speed with a longer barrel in a CO2 gun is seen in the quoted velocity for the Walther CP 88 with a 4-inch barrel compared to the Walther CP 88 with a 6-inch barrel. There is a gain of around 30 f.p.s. from the additional two inches of barrel.
What does it mean to you?
When shopping for a PCP, a longer-barreled gun will be the most efficient. If two guns of the same make get the same velocity and energy, the one with the longer barrel should get a few more shots per charge. A CO2 gun will be faster in the long-barreled versions. Compare the velocities of the S&W 586-4 with the S&W 586-6 to see what I mean.
And, now you also know that when the velocity given for a short-barreled CO2 gun is the same as for a longer-barreled version of the same gun, the velocity for one barrel length has been given for both models. Simply compare that gun's stated velocity with that of a similar gun to discover whether the short- or long-barreled model's velocity was quoted.