BB residual power calculator BB Impact Energy Calculator
This calculator let's you figure out how much residual energy is left at certain ranges and how fast the BB will travel at that distance.
This will help you know if your safety rules are inline with expectations.
Real life measurements will be slower in most cases as this model does not take into consideration the energy loss from the magnus effect (hopup) or particular added factors like wind or high humidity
BB Weight (grams)   BB velocity at X distance m/s
Muzzle energy (J)   BB impact energy at X distance J
BB diameter (mm)  
Distance in meters (m)  

The full spreadsheet with all the work can be found here for those with special interest: DOWNLOAD