I have a projectile of 4 grams, an air tank of 120 psi, a barrel length of 80 centimetres and a barrel diametre of 8 millimetres. I would like to find the ideal speed (muzzle velocity) that the projectile would be launched at, not taking into account the pressure drop, friction atmospheric pressure and stuff like that. What I did was start by finding out how much force the air from the tank would exert on the projectile. So I used Pascal's Law: F (newtons) = Pressure (pascals) * Area (metres^2). 120 psi is roughly 827371 pascals The area (m^2) - 0.004^2*pi = approx. 5*10^-5 (1/20000 or 0.00005)m^2 So F = 827371*0.00005 F = 41.37N Then I put that into F = ma to find the acceleration: a = F/m a = 41.37N / 0.004kg a = 10342.5 m/s So I have the acceleration, but how can I find how lond it accelerates for? It travels (under pressure) down the barrel for 0.8 metres, is there a calculation I can use to find the speed? Thanks for any help.