There are many reasons to upgrade from a stock bolt. Custom bolts can be quieter, so you can sneak around the field more easily. They can also provide more cushion for the ball, cutting down on breaks in your barrel. A softer bolt can even let you shoot brittler paint, which makes it more likely a ball will break when it hits an opposing player. No more of those obnoxious bounces, where you hit them, but the ball doesn't break.