You can easily turn the paintball gun you already have by adding a lengthier barrel (preferably longer than 18”), buttstock, bipod and a sniper scope.  For the best deals and most complete packages, purchase a paintball sniper that’s already put together; there are many to choose from with a wide variety of pricing. 

It’s also smart for a sniper to consider adding an electronic trigger to his sniper paintball gun; this will allow shooting options that can be tailored to the situation.  This way you will have the option of rapid, full auto firing when providing cover fire and single or 3 round bursts of paintballs for precision shooting to pick off key players.  Another fun aspect of playing the sniper is the invisibility factor; the sniper greatly benefits from blending into his environment - do this with camouflage fatigues or completely disappear in a ghillie suit.