Some fields allow you to have guns up to 425 FPS but put restrictions such as semi only on your AEG.
Some players are trusted with BA (Bolt Action) rifles that can shoot upwards of 450 FPS with .20's. However there are strict engagement distances to be maintained at all times and players running a hot BA rifle must have a sidearm for closer engagements.
Note that if you must chrono under 400 FPS with .20's. You can also chrono with .25's but you must shoot lower than something like 360 FPS (I don't think that's the real number I'm just making it up but just to get an idea), basically at 360 FPS on .25's the same amount of energy is applied to a .20 at 400 FPS. It's not the speed of the gun you're firing it's actually the amount of energy applied to the BB, think of it in those terms and you're golden.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE