These rails are mounted on paintball guns so that if people want to add extra features to their paintball guns they can attach the accessories here. For example, for laser features, the laser beam can be mounted on these rails. Also if in near future there are new and cool paintball gun accessories available in the market they do not have to worry that their paintball gun does not have these features. All they have to do is buy those accessories and attach them to these Picatinny rails. Thus they will be able to give their gun new features without having the need to buy a new gun.