I think the FPS method was adopted from paintball but in paintball 300 FPS is the regulated limit because when they were orginally test the energy the paintball exerts they placed a limit on the energy the ball is allowed to exert just under 11 ft lb. whitch was the just under the ammount needed to break a finger
Essentially the FPS limits used is a missguided attempt at safety which they didn't understand. it's all about the energy and the airsoft community needs to adopt the energy standard idea that paintball first used it just so happend that 300 FPS is what the safe energy limit worked out to.
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