John,
Thanks for the clear explanation, now I understand. I was about to start reaming my APC's. I've been using a Jett 50 FIRE but I had a chance to pick up a Nelson Q500 so I thought I would see what revs it would turn. I sport-fly Q500 and deltas so I don't have the 1-minute urgency to start. Is an APC 8.75 x 9 about right for the Nelson?