Joshua
If I were betting on a best "unmodified commercially available" prop under 6 inches in diameter for P-18, I would use an Ikara 150 mm prop. I see they are still listed in the states by FAI model supply. They weigh less than a gram without shaft, about half that of a Peck 6 inch grey plastic one.
6″ plastic indoor prop & hook Ikara | faimodelsupply.com http://www.faimodelsupply.com/product/6-plastic-indoor-prop-hook-ikara/
6″ plastic indoor prop & hook Ikara | faimodelsupply.com http://www.faimodelsupply.com/product/6-plastic-indoor-prop-hook-ikara/ Contact Us Our Story Events/Contests **PLEASE NOTE** FAI business will be closed from 9/23/16 - 10/17/16 as we are attending several contests. Orders pro...