Both the I's and II's are prone too cracking the feed neck and the pinch bolt area where the barrel goes in. Most of the time the cracks are not severe enough to keep the barrel or hopper from coming off.

The velocity adjustment is done through the bolt on the left side of the gun. To adjust it take a small hex wrench and turn clock wise to decrease (this restricts the air flow through the bolt which slow down the ball) and counter clock wise to increase.