Reason long barreled guns produce greater velocity

[BAGTIC]

Seems I am forever reading posts about how long barrels produce more velocity because there is more time for the powder to burn.

My rhetorical question is if one has two airguns exactly alike except that one has a 6" barrel and the other a 20" barrel does the longer one produce higher velocities because the compressed air/ CO2 has more time to burn?

[Terry Murbach]

NO.

[sore shoulder]

No, because the compressed air is not burning, rather it is constantly depressurizing in the barrel as the space behind the projectile increases. In a firearm the burning powder is keeping pressure behind the projectile.

[Chuck 100 yd]

There is a point of diminishing returns where more length is of no advantage and will actually slow the bullet down.
Since the air rifle bullet,like the powder driven bullet, starts from a dead stop,it takes time and barrel length to get to full velocity. any barrel length over the point of full velocity just slows the bullet back down some. Each powder has a different point where this happens.

[BAGTIC]

No, because the compressed air is not burning, rather it is constantly depressurizing in the barrel as the space behind the projectile increases. In a firearm the burning powder is keeping pressure behind the projectile.

In a firearm all the powder that is going to burn so has done so in the first 5-6 inches. After that the pressure drops steadily all along... just like in an air rifle.

[Cast Bullet Hunter]

In any firearm the bullet will continue to accelerate so long as the gas pressure exerted against the base of the bullet exceeds the force necessary to overcome friction of the bullet in the bore. This is true no matter how the pressure is derived. There is a balance point, having mostly to do with the expansion ratio of the chamber/bore, after which the bullet will begin to decelerate due to friction with the bore surface. This varies from about 12" for .22 Short, 16" for Long Rifle up to the muzzle for most calibers. Most centerfires would reach the balance point, if an infinite length barrel were possible, somewhare beyond the muzzle. For air or CO2 powered guns the balance point is shorter even than in the 22s, probably in the8-10" area.

[longhair1957]

In a firearm all the powder that is going to burn so has done so in the first 5-6 inches. After that the pressure drops steadily all along... just like in an air rifle.

That is incorrect!

Take a slow burning powder like RL-21 in a rifle and it burns the length of the barrel. Shorten the barrel and it will continue to burn after it has left the barrel (though NOT helping in velocity) But makes a large muzzle flash as the powder burns.

Now take a fast burning like Bullseye and you are correct it is done burning in a pistol caliber in just several inches.

[Don McDowell]

Seems I am forever reading posts about how long barrels produce more velocity because there is more time for the powder to burn.

My rhetorical question is if one has two airguns exactly alike except that one has a 6" barrel and the other a 20" barrel does the longer one produce higher velocities because the compressed air/ CO2 has more time to burn?

If your logic was right, a contender with a .223 super 14 barrel, and a 223 varminter with a 24 inch barrel would get the same velocity with the same loads. Fact of the matter is they don't.
Depending on the powder being used there is a point at which the difference between a 18 -20 inch barrel and a 24-26 inch barrel isn't anything to get excited about ,but there is a difference..

[Pete44ru]

[Reason long barreled guns produce greater velocity]

[This varies from about 12" for .22 Short, 16" for Long Rifle up to the muzzle for most calibers]

In fact, a 24" barreled .22 L.R. will produce less velocity than an 18" or 19" one will.

[meanc]

I've also found the same as Pete.

With the Aguila Super Colibri (primer only)
Out of a 16" 615fps

out of a 20" 590fps

out of a 23" 580fps

The longer the barrel the more the pressure diminishes and friction takes over.

Now when using 2400 / H110 / Lil'gun there is a definite increase in Velocity between shorter and longer barrrels.

[Blaine]

Even the compressed air need to escape the barrel.....the velocity stops increasing when the barrel is vented to atmosphear (the bullet leaves).

[KirkD]

As the bullet moves down the barrel the pressure drops. As long as the force exerted by the pressure is greater than the friction force between the bullet and the bore, the bullet will continue to accelerate.

When the bullet gets far enough down the barrel such that the force exerted by the pressure is less than the friction force between the bullet and the barrel, the bullet will begin to slow down.

Where that point is depends upon the amount of powder, type of bullet, etc. Certainly, no one can deny that most pistol bullets have a higher muzzle velocity out of a 20" rifle barrel than they do out of a 3" pistol barrel.

[PPpastordon]

Mostly true. However, it is not as simple as it sounds. If it were simply pressure = velocity, a load that stretched a gun to near the point of a blowup might wreck the gun, but it would fire a terribly fast bullet.
Does it? Think about it!
Isn't "if" a grand word?

[cas]

Longer barreled air guns produce more velocity, usually because they have longer compression chambers/pistons to go along with it.

[Swampman]

I have seen instances where 2 guns of the same type (different barrel lengths)were shot at the same time using the same ammo and the shorter of the 2 actually had a higher velocity.

Many factors affect velocity. Chamber dimensions and throating being 2 of them. Some powders produce pretty much the same velocity in an 18" barrel as they do in a 26" barrel.

At any rate long barrels just aren't worth the extra effort/pain. In a lever gun anything over 22" is just because you like it. I personally prefer the 18" barrels.

100fps isn't enough to matter on game.

[Kansas Ed]

I
At any rate long barrels just aren't worth the extra effort/pain. In a lever gun anything over 22" is just because you like it. I personally prefer the 18" barrels.

I disagree with that statement. I believe that the major benefit to longer barrels is the longer sighting radius.

Ed

[Swampman]

A rifle needs a scope. Sight radius is a moot point when you use one. Fighting all that muzzle weight is a major problem for me. I think 22"s is perfect.

[bogus bill]

Black powder years ago needed longer barrels. Probley another thing looked at back then was in levers some people might like the longer magazine tubes on longer barrels. How about some of those old cheap "long tom" shotguns that some people thought they needed!
Kind of the same thinking my dad had in the 50s. We wanted to get into bow hunting. Dad was a very strong athletic 6 ft 5". So he went and found a used 95 pound bow!! He soon bought a new 65 pounder!