By B.B. Pelletier
Here is a subject that gets people riled – quick! Is barrel length important in an airgun? Yes, it is, but the reasons may be different than you think.
Barrel length DOES NOT determine accuracy
There is NO CORRELATION between barrel length and accuracy. A short barrel can be more accurate than a long barrel, or vice-versa. Length alone has nothing to do with it.
Pellet control is not the issue
The people who think longer barrels are more accurate often say it’s due to the greater control the longer barrel exercises over the pellet. A barrel does not “control” a pellet in the same sense that a dog trainer controls a dog. Once the pellet leaves the muzzle, it doesn’t matter whether it has been in the barrel for 10 inches or 30; it is now a ballistic missile and subject to the same physical laws.
Proof that short barrels are just as accurate
A target air pistol such as the Aeron B99, which has an eight-inch barrel, is just as accurate as a target air rifle – like the TAU Senior – D, which has a barrel approximately twice as long. You can see this in the test targets shipped with the guns.
AirForce Airguns states that their Talon SS with a 12-inch barrel can shoot one-inch groups at 50 yards. They say the same for their 24-inch barreled Condor. Once again, this is from actual testing on real airguns.
Barrel length does influence velocity
Both pneumatic (all types) and gas-powered guns gain velocity with longer barrels. The expanding gas (or air) has more time to push on the pellet in a longer barrel. There is a limit to this, of course, but you aren’t likely to ever see an airgun barrel long enough to reach it.
Cardew determined optimum spring gun barrel length
A spring gun gets all of its “push” in the first few inches of the barrel. Gerald Cardew pointed out in The Airgun from Trigger to Target that only the first six inches of the barrel is needed for a spring gun to achieve maximum velocity. His experiments were conducted in the mid-1970s. Although technology has advanced since then, today’s spring-piston guns probably don’t use more than the first 10 inches of barrel for top velocity.
After that, the pellet coasts the rest of the way. Yes, friction with the bore slows the pellet somewhat, but the amount is so small that it doesn’t amount to anything. Spring gun barrels are made longer than 10 inches because they are used as levers, as in breakbarrels. And, on all rifles, a shorter barrel just doesn’t look right. That’s why the underlever TX 200 from Air Arms hides its nine-inch barrel inside a longer shroud that also muffles the sound of the shot.
I will address the important contributors to accuracy in future posts. I think we all would like to know more about the subject. I will also suggest some tests that you can conduct on your own to determine the best accuracy for your airguns. It will take several posts to get it all, so there is something to look forward to.
So, airgun barrel length is a factor in performance, but accuracy is not directly affected. Some people may still not believe this, but all the literature I have read and all the tests I have done show it to be true. Any thoughts?