On July 18, 1993, at 1030 mountain daylight time, a Zbacnick Challenger II homebuilt airplane, N851BZ, was substantially damaged during a forced landing near Alamogordo, New Mexico, following the inflight separation of the propeller. The commercial pilot, sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed for the local personal flight. According to the pilot, a slight loss of RPM was experienced while maneuvering in the local area. The engine continued to operate normally after the throttle was advanced to reestablish normal power. The pilot further stated that approximately ten minutes later, a slight vibration developed, followed by the departure of the propeller assembly. While attempting to land on an open field, the pilot overshot the landing area and the airplane impacted the top of a berm at the end of the strip and bounced. Examination of the airplane revealed that the propeller bearing had seized resulting in the separation of the propeller. The winds at the time of the accident were from the west at ten knots, gusting to 17 knots. The wreckage was verbally released to the owner by the Federal Aviation Administration inspector at the accident site.