On March 25, 2002, about 0720 mountain standard time, a Piper PA-18-150, N22EV, sustained substantial damage after colliding with terrain near Fort Peck, Montana. The airplane is owned by the pilot, and was being operated as a visual flight rules (VFR) flight under the provisions of Title 14, CFR Part 91. The commercial pilot-in-command and passenger sustained serious injuries. Visual meteorological conditions prevailed and no flight plan was filed. The pilot was conducting a predator (coyote) control flight over private rangeland near Fort Peck. During the flight, at a reported altitude of approximately 40 feet above ground level (AGL), the passenger inadvertently discharged a semiautomatic 12-gauge shotgun. The pilot, who was seated in the forward seat, reported that the gun fired 3-4 times, striking the right wing, fuel tank and aileron assembly. He reported that the damage resulted in a loss of aileron and elevator control. The airplane entered a descending turn to the right and subsequently impacted terrain in a nose-low attitude. The pilot reported the aircraft was on fire upon touchdown and continued to burn after the impact. The pilot reported that there were no preexisting mechanical malfunctions or failures that contributed to the accident.