On Wednesday, March 31, 2004, approximately 0945 mountain standard time, a Cessna 305A (L-19), N5210G, impacted the terrain during an inadvertent landing roll ground-loop at Bozeman Municipal Airport, Bozeman, Montana. The private pilot, who was the sole occupant, was not injured, but the aircraft, which is owned and operated by a family member of the pilot, sustained substantial damage. The 14 CFR Part 91 personal pleasure flight, which departed Helena, Montana, about 45 minutes earlier, was in visual meteorological conditions at the time of the accident. No flight plan had been filed. There was no report of an ELT activation. According to the pilot, the flare, touchdown, and initial part of the landing roll in the tail wheel-equipped aircraft were normal and uneventful. But as the aircraft slowed, it suddenly swerved to the left, and the pilot's attempts to realign it with the runway were not successful. The aircraft therefore exited the left side of the runway and entered a ground loop. During the ground loop sequence, the right main gear leg partially folded under, and the right wing collided with the terrain. A post accident inspection of the aircraft's braking system, rudder system, and tail wheel did not reveal any evidence of a malfunction or anomaly that would have contributed to a loss of directional control.