On May 4, 2006, about 1930 central daylight time, an amateur-built Bangham Barracuda, N91LB, piloted by a private pilot, was substantially damaged during an emergency landing at Monett Municipal Airport (M58), Monett, Missouri. The personal flight was being conducted under 14 CFR Part 91 without a flight plan. The pilot and passenger were not injured. The local flight departed Aurora Municipal Airport (2H2), Aurora, Missouri, about 1820. The pilot reported that approximately 8 minutes after takeoff, while conducting a series of climbs and descents, he heard a "pop" and smelled hydraulic fluid. He noted that the landing gear in-transit light illuminated. He selected gear down, however, only the right main landing gear extended properly. The nose gear and left main gear remained retracted. Use of the emergency landing gear extension system was not successful. The pilot set up for an emergency landing. On short final he reduced power in order to secure the engine prior to touchdown. He stated that with the power reduction the airplane "dropped out of the sky." The airplane subsequently landed on a grass area short of the runway and slid approximately 120 feet before coming to rest. During this time, the extended right main landing gear collapsed. A post accident inspection revealed that a hydraulic line on the firewall had ruptured. During follow-up testing, the hydraulic pressure switch and emergency gear extension valve both operated properly. The piston rod within both the nose and left main landing gear extension cylinders was bent preventing free movement. According to the pilot, the landing gear system utilized hydraulic pressure to raise and hold the gear in the retracted position. No up-locks were installed. Emergency gear extension was normally accomplished with the assistance of gravity when hydraulic pressure was released by actuating the emergency extension valve. The pilot reported that because of the electrical installation of the landing gear limit switch and the hydraulic pressure switch, it may have been possible for the hydraulic pump to be energized regardless of system pressure. In that situation, the pressure switch would not protect the hydraulic system allowing it to become over-pressurized.