"All Mossberg models including the 835, 535, 500, 505 and 590 (except for Special-Purpose and Law Enforcement models) are shipped with a wooden dowel with two rubber O-rings, also called a duck plug, located in the tube magazine. This is to comply with U.S. migratory bird laws. This dowel reduces and regulates the number of shells that can be loaded in the magazine to 2."