A guy named Nathan Allen has done a fantastic study on airsoft BB physics called the "Airsoft Trajectory Project." His calculations, tables and formulas are very thorough, and cover the following principles:
-BB characteristics, volume, density and terminal velocity
-air density
-kinetic energy
-drag force
-magnus force
-spin decay
-drag coefficient
-lift coefficent
-gravity
-effects of hop-up
-effective and maximum range determinations with all weights of BB's, 6mm and 8mm
-effect of wind on trajectory
-headwind/tailwind component
-crosswind component
-effect of altitude on trajectory
-effect of temperature on trajectory
-determining muzzle energy
-safe impact energy
-recommended minimum engagement distances
-velocity comparisons of BB's using equal masses
-mass comparisons of projectiles fired at equal energies
i have never found any better info ever on the physics of airsoft. i encourage you to check out his information.
his study can be found here:
http://cybersloth.org/airsoft/trajectory/index.htm