This invention is a barrel attachment attachable to the firing end of the barrel of a compressed gas gun and a method of using the same. The barrel attachment allows a user to spin a projectile fired from the gas gun just before it exits the barrel attachment. This spin alters the projectile's normally straight trajectory; in other words, it makes the projectile curve. The barrel attachment is adjustable. In the preferred embodiment, the user or shooter can adjust the amount of spin and thereby the amount that the projectile curves by rotating an adjustment sleeve about the barrel attachment, which causes contact pads to protrude into the passage of the barrel attachment. In the preferred embodiment, the user can adjust the direction of curve by rotating the barrel attachment about the gun barrel.