Get an electro penumatic gun, something low pressure. It will put less stress on the paintball.
Grab a longish barrel, despite people saying otherwise, a longer barrel is more accurate. I wouldn't go too long, a 16'' barrel should work very nicely. (though stay away from the flatline, they are horribly inaccurate. Plus, after a certain range, paintballs don't even break and all you did was bounce a paintball off of them and give away your position or at best made them aware someone was shooting at them.
OVERBORE OVERBORE OVERBORE
Grab a large bore barrel, the ball never contacts the side and doesn't develop a spin to one direction or the other causing it to go awry. It will ride a cushon of air out of the barrel.
Personally, I would grab a 16'' custom products .691 barrel.
Mount that on top of a proto rail, it is a cheap light gun and will run low pressure and consistent.