On June 17, 2002, approximately 0900 mountain daylight time, a Cessna 180K, N66471, registered to and being operated/flown by a private pilot sustained substantial damage during a loss of control/ground loop while executing an aborted takeoff at the Helena Regional airport, Helena, Montana. The pilot and pilot rated passenger were uninjured. Visual meteorological conditions existed and no flight plan had been filed. The flight, which was personal, was operated under 14CFR91 and was planned as a local flight. The pilot reported to an FAA inspector from the Helena Flight Standards District Office that during the takeoff on runway 16, which is 2,980-foot long, the aircraft accelerated normally until reaching approximately 40 knots. He then felt that the aircraft did not have sufficient airspeed and he initiated an aborted takeoff. As he applied brakes after touching down on the remaining runway the aircraft swerved left and ground looped and the right wing outboard of the flap/aileron seam impacted terrain. The pilot later reported that he decided to abort the takeoff about one-third of the way down the runway. He retarded the throttle to idle and then "...brakes [were] gently applied, [with] no obvious response. More firmly applied. [The] left brake grabbed, [the] plane began to turn to left. Right [brake] applied more firmly [with] no response. Right brake repeatedly firmly applied but [the] plane continued to turn left; no apparent response to right brake attempts..." (refer to NTSB Form 6120.1/2). The winds were calm at Helena Regional airport at the time of the accident and the pilot rated passenger reported that the runway was "damp." A mechanic examined the aircraft subsequent to the accident and reported that both brake discs appeared to be "overheated." The left wheel still rotated and stopped with the application of left brake. The right brake could not be tested in this fashion as it had separated from the airframe. The parking brake was found disengaged and functioned satisfactorily following the accident.