its a lot more complex than that,
the paintball has a parabolic motion, so
its impossible to work out how far it will travel without an angle
at 300fps thats 200mph (give or take) which is around 100 metres per second
its really hard to explain without a diagram
ball will start going horizontal........ like so.......... ------->
then it will curve, and its motion will be split up into 2 components,
its velocity will then be (v cos @) **with @ representing theeta** (cos because its the horizontal part of the motion)
so you know the speed it travels
but you still need to know the angle it is shot at and the time taken for it to hit the deck