The barrel length is mostly associated with accuracy, as a longer barrel will stabilize the projectile longer and therefore creates a straighter trajectory. While this is basically true, this effect is most probably a bit overrated in the realm of airsoft. Much more important is the length in relation to the volume of air that is compressed in the cylinder. If the air volume is too high for a certain barrel length, the BB will still be accelerated shortly after it left the barrel, which possibly destabilizes the flight path. If the air volume is too low, the BBs canít be fully accelerated, wasting potential velocity. Therefore various cylinder designs are available, bore-up ones with a bigger volume as well as those with holes at different areas, reducing the utilized volumes to match the respective barrel length.
Another difference the length can make is the muzzle velocity. The longer the barrel, the later the BB will leave the barrel and the longer it will be accelerated, provided the air volume is sufficient to use the length. Another tricky behavior here is again the difference that various BB weights can make to the muzzle energy. If a heavier and a lighter BB is used in the same barrel, the heavier one is travelling slower and therefore stays longer in the barrel, giving it more time to accelerate (again, provided the air volume is sufficient). This means that a heavier BB, although its muzzle velocity is still lower compared to the lighter one, will have relatively more muzzle velocity than it should have according to the velocity conversion explained in the beginning of the article. Thus it has effectively more muzzle energy than the lighter BB fired from the same gun. This is something that should be considered while checking fps limits for a game. This effect is even more common with gas guns, as the amount of propellant per shot in those guns is most often much higher that than needed in stock configuration, meaning that nearly every increase in barrel length and/or BB weight will result in more muzzle energy.
The barrel diameter has quite similar effects. A tighter bore results in less leaked air, meaning that more air is utilized to accelerate the BB, thus it creates a higher velocity. The effects on accuracy however are quite debated. One could assume that a tight barrel will stabilize the BB better than a loose one, however much more relevant is the regularity of the inner surface. Also a certain amount of air cushion is needed to prevent the BB from touching the barrel surface, which would destabilize the trajectory as well as the amount and angle of the backspin, created with the hopup. So too tight is as bad as too loose.
- World Airsoft News - Read full article: http://www.airsoft2day.com/news/26-t...#ixzz250RyEqce
Hope this helps