GunThe distance a paintball can fly is directly dependent on the speed a ball is traveling when it leaves the barrel. Since safety dictates that a ball leave the barrel at under 300 fps, very few upgrades will increase the distance that you can shoot from. The Tippmann Flatline (compare prices) barrel can add a certain amount of back spin to the ball and slightly increase your range, but from my experience, the increase in distance is not extremely beneficial because your accuracy will decrease the further you shoot.
Since most guns shoot about the same distance, be sure that you find a gun that is accurate and consistent. The key to being a good sniper is the ability to hit your target on the first try. A gun that does not consistently shoot the same speed or if there is significant variation in where the ball goes from one shot to the next will not allow for one-shot kills which are vital to the position. Look for guns with regulators (or expansion chambers if you use CO2) and read reviews to find out how accurate guns are. Additionally, be sure that your gun is not brightly colored - you need something that blends into the surroundings and does not stand out.barrel is better than the competition's, but the truth is somewhat different. Accuracy is more dependent upon the consistency of the gun shooting the ball, and any one barrel will not greatly improve performance if there is a good paint to barrel match. Choose whichever barrel you like, but make sure your paint properly fits your barrel.