I maintain a small piece of software for the Airsoft/Paintball community. I include some basic energy and velocity calculations but I have also as of a few versions back started including more "theoretical" calculations like how far a BB will travel and that sort of thing. I want to improve the calculations I am using to be more accurate and take drag into account. I've taken some physics but we just touched fluid dynamics a little bit. I have been trying to get together the equations and information I will need to translate all of this into code. So far I have been able to find equations for drag coefficients and the drag equation, but honestly I don't really know how to use these. For calculating my drag coefficient I can easily find things like the mass density of air and so on, but it's the stuff specific to my object that I have problems with. Would someone please explain to me the process putting all the information I have into these equations?