This is not an easy task and can only be done with some accuracy by applying exterior ballistics software. There is a simple formula for estimation purposes. z = k1*T2 T is the total flight time in seconds k1 is a factor in the area of 0,1 … 0,12 m/s2 which depends on spin, muzzle velocity and bullet parameters z is the side deviation in meters Generally bullet drift at short distances (100 – 300 yd) is by far smaller than the normal scatter. Drift is only of some practical importance for artillery shells, at ranges of several miles.