[lurkingknight]

basic determining factors of fps in aegs (assuming no short stroke) is air cylinder volume, barrel bore and diameter and spring strength. Other factors may include if the spring guide is plain or has a bearing, if you have a spacer/bearing on the piston head and how thick it is. If your air seals are good throughout with the right setup, you can get 400 fps on a m100 spring as you have observed. This is why when people ask what spring they should get to get x fps, a good tech can't answer that immediately, they need to know the other factors, and even then that's not to say you don't get a mislabeled spring or you have a mutant gun. I've seen m100s get as high as 410 in some guns and 350 in others.