On August 26, 1996, about 1120 eastern daylight time, a Cessna T303, N420FC, overran the side of runway 16 at the Big T private airstrip, Senoia, Georgia. The airplane was operated by the owner/pilot under the provisions of Title 14 CFR Part 91, and visual flight rules. A flight plan was not filed for the personal flight. Visual meteorological conditions prevailed. There were no injuries to the commercial pilot, the only occupant, and the airplane was substantially damaged. Origination of the flight was Peachtree City, Georgia, about 1128, on the same day. The pilot reported that he departed Hilton Head Island, South Carolina, and proceeded under instrument flight rules (IFR) to the final IFR fix for Big 'T' Airport. At PECAT, the final IFR fix, the pilot entered holding for about one hour, while waiting for an undercast to clear. He then landed at Peachtree City, fueled the airplane, and checked weather with personnel at Big 'T' Airport. He departed and flew the five miles to Big 'T' Airport, in visual conditions. On landing, according to the pilot, the airplane ran off the runway into an adjacent ditch because "braking action was insufficient to stop aircraft." According to the inspector who visited the accident site, the airplane overran the side of the 2100 foot long runway. The airplane touched down about 1/4 of its length and veered off the runway after rolling about 75-80% of its length. The airplane's flaps were extended. The runway was level sod with grass about four to five inches long. According to the pilot there were no mechanical malfunctions, the airplane simply began sliding, continuing off of the runway.