An anti-chop system for mechanical paintball markers includes an optical sensor in the breech that detects presence of a properly seated paintball in the breech for launch. When such a paintball is not detected, a control circuit communicates with an actuatable structure that physically communicates with a paintball marker component that moves as part of the firing and launch of a paintball. For example, such an actuatable structure is a lever arm that communicates with the bolt or trigger to prevent the firing operation of the paintball marker when a paintball is not ready for launch.