There are many many threads on all the diffrent forums about this and basically it boils down to the following .
you need at least 8" of unported barrel to get the ball up to speed and after that just a few inches to give the ball some accuracy so 10 - 14 inches is about the optimal length anything more then 14 is just a waste and will just use more gass and won't make any real diffrence for accuracy. As many people have said 12 is the most common it will give good accuracy (providing you have the right paint match) and is manoverable in tight situations.
you need at least 8" of unported barrel to get the ball up to speed and after that just a few inches to give the ball some accuracy so 10 - 14 inches is about the optimal length anything more then 14 is just a waste and will just use more gass and won't make any real diffrence for accuracy. As many people have said 12 is the most common it will give good accuracy (providing you have the right paint match) and is manoverable in tight situations.