The results definitely vary on the gun, both in parts used and how they are tuned. Most that I've come across fps goes down when not holding the pump. My regular gun, there is no difference. I've had one where not holding the pump caused an increase in fps. Made me look like an idiot. I was explaining to the guy why he should hold the pump forward when chrono-ing. His gun wasn't very consistant, but the average fps went up around 10fps. Weird.