fps can be misleading. if you know some basic phsyics you should know about inertia. Even though the .25g is traveling slower it will still hit with the same if not more energy *AKA joules*. In all honesty this is what we should be using and not FPS for field limits. That way you can be "cronoed" in on any weight of BB.
Long answer short, you need a spring or a velocity reducer but I have heard those are crap.