C550 single pilot Captain reported a runway excursion into the over run area when attempting to land in moderate rain. The Captain selected the anti-skid on; in accordance with SOP; but the brakes were not responding during the landing roll; resulting in a slow speed excursion at the runway end into the over run area. There was no injuries or damage to the aircraft.

Narrative

Upon landing at ZZZ in moderate rain; I applied brakes with little response. I was contemplating on rejecting the landing when the brakes started responding and I felt we had plenty of runway remaining to come to a stop. This airplane does not have reverse thrust; so that option was not available. Then a few seconds later; the brakes appeared to release and quit decelerating. By this time; I was too slow to reject the landing with the runway remaining. Anti-skid was on and I was continuing to brake; but the brakes just were not responding. We went off the end of the runway into the overrun at a relatively slow speed. There was no damage to the airplane or any airport structure. No persons were injured or even upset. My personal feelings are that this is a first generation anti-skid system that maybe only releases the brakes. Procedures call for anti-skid on before take-off and off after landing. I believe I would have had better braking action with the anti-skid off for the runway conditions that existed at the time.