Hello, I'm a college student in the last semester of my second year working towards my degree in Mechanical Engineering. I'm working on a project for my ODE (Math-222m) class involving the mathematical modeling of the internal ballistics of the common Spring/Air pellet rifle. I've got basically all the necessary physics formulas down for building the model (Spring Energy Equation / Ideal Gas Law / Linear Kinetic Energy / Rotational Kinetic Energy / etc.) except for one. I need a formula for the work done (obviously negative work done) by the bore friction during the pellet’s trip down the barrel. I've done a lot of searching but so far have yet to dig up any hard math or even imperial data -- All I've found so far is general references. Example, "Our pellets; due to their special . . . . coating reduce bore friction significantly and can result in some cases of a velocity increase of up to 20%" That don't help me at all I need the hard stuff, not this watered down junk. So far I’ve learned that there seems to be a direct relationship between the magnitude of the contact surface between the pellet and the barrel and the magnitude of the bore friction force opposing the pressure force induced by the compressed gas. This contact surface could be easily built into the model as a property of the individual pellets but I need a way to calculate the magnitude of the resulting friction force. Help !!!