I will have to disagree though that you can't go wrong with 12 to 20. And the simple truth is that I have been on many fields where the balls would break inside any barrel over 12. Those players with 8-12 (but more around 10 or so) had very little issues.
And also given that you only need an 8-10"a control area, anything over that is overkill unless it is for porting (for reducing noise), for sight alignment (as mentioned) or for looks.
Also consider that you can not make any true comparisons between barrels and efficiency by just looking at porting and length VS no porting and length. You also have to take into consideration the barrel size and that of the balls themselves.
I will also point out that paintballs do not warp as much as folks think they do when fired and you still only need a certain length for them to expand and then gain their original shape. This does not change significantly due to temperature. So you will not see any noticeable difference in that respect with a 10" or a 16" barrel.
And furthermore, once the ball has reached it acceleration point, anything after that will cause drag on the ball should the ball touch the barrel. It can also cause the ball to go in a direction which was not intended. This is seen quite often with large boar mussel loading muskets of the flintlock era. And it can be seen with paintballs as well. So you need to find your balance.
The real problem is that folks want ideal situations all the time, and they are seldom to never found. And another problem is that people take what they perceive to be happening and assign it as a constant rule when in most cases what they think is happening isn't happening at all. Perception is a selling point for many paintball products, in spite of truth.
Good thought process though WarCowboy. I just think some things are not quite as you believe them to be concerning what is really happening. But your points about USE and length are dead on. Those are different issues though, but BOTH important for folks to consider when deciding what length (or even bore size) barrel they should use.
