sentry vertical capability..

is there any way to tell how far the sentry can fire up or down.... From the roof of B in gravelpit inside? from the bottom of 3rd stage dustbowl canyon to the top?

is there a way to tell for sure without building a sentry and trial and errorr?

When you have the toolbox for the sentry out you have a shere grid around you, its blue for blue and red on the red team.  This is the range of the sentry, if you cannot see the grid that means it can hit it because the sphere is being drawn behind what you're looking at.

Be careful when relying on a sentry to track targets below it - many areas in the game have a glitch where the sentry will shoot into the floor if the target moves below its horizon, wasting ammo and stopping it from retaliating if another enemy approaches from a new direction. If you're going to build a sentry which can see low areas, make sure to put it as near the edge of the ledge as you can to avoid this - or know which spots can cause it and which can't.

oh its a spere? i thought is was a cylinder lol

The sentry has no vertical limitation.  However, if you are too high or too low, the target will be out of horizontal range from your sentry very quickly due to the fact that your sentry is probably on a wall or building up above the place your enemy is coming from.  So by the time the enemy exits from the building and runs into the open below you, your sentry has very little time to target, and then shoot the enemy.

Also, it is very difficult for the sentry to correctly lead a target from very far away, and so the sg will miss a moving target at a great distance if the target has much speed at all.

This is one reason why the sg up high above the last point of well is so useless.  Also the point you have to put the sg on is too far away to hit the cap point itself.