Originally Posted by CDN_Stalker
That's only an fps/weight to joule converter...
No it's not, it also converts backwards as well. Check it out again - the second button does a reverse calculation.
Enter 460 as the first FPS and 0.20g as the BB Mass and hit "Convert FPS to Joules".
At the top, you will see your answer: "A 0.20g BB leaving the barrel at 460 fps will contain approximately 1.97 joules of energy."
Now in the second section, enter 1.97 as the energy and 0.30g as the weight.
This is the answer returned: "A 0.30g BB containing 1.97 joules of energy will leave the barrel at approximately 376 fps."
Therefore: 460-376fps = an 84fps drop by switching from 0.20g BBs to 0.30g BBs.
As mentioned already: keep in mind that this is NOT a valid way to make your gun gameable if you exceed velocity limits. You will still exceed allowable field limits due to the energy exerted.