On June 24, 2001, about 0705 hours Pacific daylight time, an experimental Stolp Starduster SA-300, N711MH, operated by the pilot, veered off runway 27R and ground looped during landing rollout at the Gillespie Field, El Cajon, California. The airplane was substantially damaged. Neither the private pilot nor the pilot-rated passenger was injured. Visual meteorological conditions prevailed, and no flight plan was filed. The personal flight was performed under 14 CFR Part 91, and it originated from the field about 0650. The pilot reported to the National Transportation Safety Board investigator that during the flight he was becoming familiar with the airplane because he intended to purchase it from the pilot-rated passenger/owner. The pilot indicated that he applied too much rudder during his final landing. After the airplane veered off the runway, the lower left wing contacted the ground and broke. A subsequent inspection by a local airplane mechanic revealed the outboard portion of the lower left wing's aft spar was cracked, and the left main landing gear was broken. The mechanic stated that it appeared the gear had been subjected to an excessive side load. No evidence of corrosion or metal fatigue was noted in the area of the broken axle.