A joule is a measure of energy, You might have read this on the box of your Airsoft gun. *Under one Joule* or *Over one Joule*.
I bet you wondered how many FPS a Joule is?.
Well, It's 328 FPS or 100m/s (Meters per second).
The reason they use a Joule is because it's the energy needed to propel a pellet at a humans eye and penetrate it. You'd be blind. But don't forget!, The pellet does not need to penetrate your eye to cause blindness.
Also, Here. In Ireland. Any pellet gun over one Joule is NOT ALLOWED.
So, if your going to get a pellet gun over 328 FPS and your in Ireland.
Too bad.
-IrishaAirsoft