1. A method of predicting a future muzzle velocity of an indirect-fire weapon, the method comprising measuring a muzzle velocity and using a Kalman filter in combination with a first round prediction algorithm in order to predict a future muzzle velocity, wherein said Kalman filter is a multi-state Kalman filter that functions to estimate major sources of errors in muzzle velocity prediction and said Kalman filter utilizes: A) a definition of the errors and their stochastic behavior in time; B) the relationship between the errors and the measured muzzle velocity; and C) how the errors influence the prediction of muzzle velocity.