On July 4, 2002, approximately 0845 Pacific daylight time, a homebuilt Welborn Pulsar XP, N777XP, registered to and being flown by a private pilot, was substantially damaged during landing at the Prineville airport, Prineville, Oregon. The pilot was uninjured. Visual meteorological conditions prevailed and no flight plan had been filed. The flight, which was personal, was operated under 14 CFR 91, and originated from a non-airspaced landing site approximately eight miles southeast of Prineville approximately 0830. The pilot reported that he departed the landing site en route to Prineville to practice landings at the Prineville airport. Upon arrival he conducted his first landing successfully. The pilot reported that during the second landing on runway 28 the throttle "came off in his hand," the engine went to full power, and the aircraft bounced back into the air and then returned to the runway surface. The pilot then shut the engine down as the aircraft began veering left and all three landing gear collapsed as the aircraft departed the runway. The aviation surface weather observation for Redmond airport 11 nautical miles southwest of Prineville near the time of the accident was reporting the wind as coming from 020 degrees magnetic at 5 knots.