How do different barrel lengths affect accuracy?

[intrepidaf]

I'm new to airguns and looking to understand more about how different barrel lengths affect accuracy. Can anyone explain the relationship between barrel length and shot consistency?"

I found some info on this forum and google regarding the subject but was unsure of which were true.

1. Longer barrels always result in better accuracy: While barrel length can influence accuracy, it's not the only factor. Factors like barrel quality, ammunition used, and the shooter's skill also play significant roles.
2. Shorter barrels are always less accurate: While longer barrels can provide more stability to the projectile, shorter barrels can be just as accurate if they are well-made and properly calibrated.
3. Barrel length directly correlates with projectile velocity: While longer barrels can potentially increase projectile velocity due to more time for the gas to act on the projectile, other factors like air pressure, barrel quality, and projectile weight also play roles in determining velocity.
4. Barrel length is the most important factor in accuracy: While barrel length is important, factors like barrel quality, bore consistency, and the quality of the ammunition are equally important in determining accuracy.
5. Shorter barrels are always louder: While it's true that longer barrels can sometimes help dampen the sound of the shot, factors like the type of airgun and the air pressure used also influence noise levels.

 

[Caliber 22]

Many long distance shooters found that longer barrels give better ES and thus better SD as things get a chance to calm down and equalise.

 

[Caliber 22]

I used to struggle a lot with the consistency of my pcp. With any minor change in temperature there was a major change in POI. That was because with temperature the barrel sat in a different way and the vibrations was different. After some things I did it is much more consistent and in cold or hot weather the POI is now the same. Also, it is not pellet speed sensitive as before, the harmonics is more in control regardless of the speed.

 

[JDGriz]

@calliber22 I wonder if this isn't just less susceptibility to movement caused by recoil, where it exists. A sort of archer's paradox but for barrels - the front of the barrel's movement lagging behind the back of the barrel, particularly when and if it's weighted and/or long. It's all then less susceptible to differences in stock pressure, support etc.
Harmonics do come into this, but only to the extent that extra weights make them even less the case in the duration of a shot.

 

[Caliber 22]

Harmonics is 100% a factor. That is also why long distance competition PB barrels are thicker than sporting / hunter rifle barrels as there is less harmonic differences during slight differences in cartridge load. It is obvious that a big PB has a lot more recoil than pcp's, yet it can be tuned to a 1/4 MOA and less precision no matter the barrel length. Look at the following high speed video of barrel movement from a PB. There is no way a pcp will have more movement because of recoil. Recoil is first straight backwards and after the bullet is long gone, recoil will have the barrel moving upwards because of asymmetric nature of the rifle and the shooter holding it.

Video window is in 3 parts, top part show the receiver with the hammer at the rear in yellow.
Middle part show the full length barrel
and bottom part the barrel tip.

Description of what is happening is in the writing below the video.

 

[dizzums]

the way i see it, mainly, a barrel that is beyond the length that is increasing efficiency and speed actually slows the projectile down with all the associated factors that are introduced with that situation .. outside of that i think a longer barrel steadies everything, as long as the gun in question can push the ideal velocity out of it ..

 

[Caliber 22]

With centre fire PB super sonic ammo and slow burning powder, longer practical length barrels will not slow down the bullet. Subsonic or near subsonic rounds might slow down the bullet. With .22LR they use fast burning powder and it will mostly be completely burned at anything between 10" and 14" but that does not imply that the pressure behind the bullet just disappear, there is still pressure until the bullet leaves the barrel, it just get less and less. With pcp's you can tune the rifle to suite any length barrel that is on the rifle, that is why some people prefer longer barrels for slugs so they can tune it for higher speeds not possible with a barrel that is to short. Look at most of the big bore hunting pcp's, they mostly have long barrels. FX have barrels up to 800mm, maybe longer that I don't know of, and that is for heavy slugs. With a pellet you can tune a short barrel rifle to get maximum pellet speed with high reg. pressure. The longer the pellet barrel the lower reg pressure you can use for the same speed.

 

[Caliber 22]

The next 2 videos is for a "slightly longer" 308 and .22LR to test what the speed for different barrel lengths are. I don't know of such a video for PCP rifles.

 

[cavedweller]

IMO - all of the comments are somewhat correct but only to a point... there are so many factors that affect a barrels ability to be accurate that you can't just assign one attribute like the length... a make a absolute statement of fact. @Ballisticboy would probably like this thread....