A formula for calculating recoil velocity involves understanding the relationship between the mass of the projectile and the mass of the gun. The discussion suggests that the fraction of the gun's mass represented by the projectile (Mp/Mg) can be used to determine the gun's rearward acceleration based on the projectile's forward acceleration. Specifically, if Mp/Mg equals a certain fraction (n), then the gun's acceleration (Ag) can be calculated as the projectile's acceleration (Ap) multiplied by that fraction. This approach provides a conceptual framework for calculating recoil velocity without complex mathematics. Overall, the discussion highlights a basic method for estimating recoil based on mass ratios and acceleration.