How to identify a centerfeed barrel??

[Target]

Greetings,
How does one identify a centerfeed barrel from a left/right one?

Dan

[paintman1142]

the little rail thet the twist lock assembly sets in to (the part that runs along with the lenght of the barrel) will be about 90 degrees either left or right of the center of the hole for the paintballs.

OR: the part of the rail that runs perpendicular to the will end in the other side of the barrel from the center of the ball hole.