Monday, April 04, 2005

Is airgun barrel length important?

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.

Summary
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?

15 Comments:

At June 30, 2005 12:38 PM, Anonymous Anonymous said...

what about choked barrel ?

 
At June 30, 2005 1:29 PM, Blogger B.B. Pelletier said...

Did you read the posting from June 17? If not, I may have answered your question(s) there.

If you have other questions about choked barrels, please post them.

B.B.

 
At August 19, 2005 8:40 AM, Blogger Markoff Chaney said...

In that barrel length may be a determining factor of sight radius, wouldn't it be important to accuracy?
Yeah, I know, even the pros go round and round about the importance of sight radius to accuracy, but it is arguable that a longer sight radius reduces faults on the target resulting from normal sight deviation.

 
At August 19, 2005 8:45 AM, Blogger B.B. Pelletier said...

Markoff,

I agree that sight radius (the separation of front and rear sights) is important to a shooter's ability to shoot accurately. All I was commenting on in my posting was the inherent accuracy of the gun itself.

B.B.

 
At October 24, 2005 10:02 PM, Blogger Kdrake said...

What about bullpup designs in an air rifle? I have only seen a few air rifles like that and i dont think any are true bullpups like the crosman nightstalker.

 
At October 25, 2005 4:50 AM, Anonymous B.B. Pelletier said...

Kdrake,

The Tech Force 89 is a bullpup springer. Besides that, I don't know of any, either.

B.B.

 
At October 29, 2006 9:36 PM, Anonymous Anonymous said...

BB- You are right. Some time ago l removed 4.5" of a (scoped) Gamo Shadow barrel. l wanted a more compact woods rifle. Anyway it has not lost any speed or accuracy, thank god, because it never was much better than a 1" at 25 yard rifle. By the way l get several thousands of a inch scope base movement with each shot, even with there scope stop, any advice-Thanks

 
At October 30, 2006 6:36 AM, Blogger B.B. Pelletier said...

Gamo scope stop,

As long as the scope stop is mechanical and not just clamping pressure alone, the movement will eventually stop. Your scope is probably just seating itself against the stop.

B.B.

 
At December 02, 2008 3:22 PM, Anonymous Anonymous said...

B.B.

Did you ever write an article and talks about how to make an accurate airgun barrel or what makes an airgun barrel accurate ?

I cannot find such article.

Thanks,
Joe

 
At December 02, 2008 3:33 PM, Blogger B.B. Pelletier said...

Joe,

I did a report about rifling, which concentrated on how it is done. But I doubt I've written an article about making an accurate airgun barrel or what makes a barrel accurate.

While I do know some things that we all like to see in barrels, I'm not sure they constitute everything that makes a barrel accurate.

I know a little more about firearm barrels, only because more has been written about them. But I'm no expert. Maybe a person who can conduct a conversation for a while.

B.B.

 
At December 24, 2008 9:39 AM, Blogger phillbilly said...

Hi bb just bought a s/h theoben fenman now i was concerned about the accuracy of its very short barrel(about 8") but i found out this rifle is able to produce half inch groups at 40 yards @ 12ftlb its been a while since i have shot air guns so with practice i hope to achive this with the help of your advice and plenty of practice and what a lovely gun far more rewarding than precharge.

 
At December 24, 2008 10:36 AM, Blogger B.B. Pelletier said...

Phillbilly,

Good report!

B.B.

 
At January 22, 2009 8:33 AM, Anonymous Herb said...

B.B.,

For springers doesn't a barrel longer than 10 inches decrease accuracy?

The extra length would seem just to give the barrel more time to move around due to recoil. It seems springer barrels should be designed to get pellet flying in 10 inches and them have a shroud to be the lever.

Can't hep but wonder how well a TX200 would do with a full length barrel.

Herb

 
At September 02, 2009 2:01 AM, Anonymous Anonymous said...

Does this same principal apply to big boars?
Would a barrel extension on a .50 Dragon slayer increase velocity on a 275 grain bullet?
If so then WHERE CAN I FIND an extender for the Dragon Slayer??
Thanks!!

 
At September 02, 2009 6:38 AM, Blogger B.B. Pelletier said...

Physics is the same for all guns, regardless of the caliber. Yes, a longer barrel does add velocity to a big bore.

There is no such thing as a barrel extension. You need a new, longer barrel and it will probably cost as much as the gun, since it will have to be custom-made.

If you are still interested in this topic, I can write a special blog report about it for you. I am in New York filming a television show through Friday, Sep. 11. If you will contact me on the current blog after that, I will write the report.

http://www.pyramydair.com/blog/

B.B.

 

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