A lot of the performance pistons use only one ring. From what I understand it's to reduce drag. I know some of the old racers would leave the bottom ring off a conventional piston for the same reason. I'm not convinced that it's worth the small amount of performance you gain in exchange for engine life. There should be a spec for ring end gap, usually .008" to .012" or so. If the gap is too small, the engine won't last ( speaking from personal experience).
Stuck in the seventies- not in the swamp.
(6) Attex, a Hustler, a Super Swamp Fox, (2) Tricarts, (3) Tri-sports, a Sno-co trike, 3 Dunecycles, and a Starcraft! ...so far