to put it simply, it has to do with follow through. as many have found out, rifles poi can change from one shooting position to another and that rifle average velocity can change up to 50 fps. i cant scientifically explain thing extensivly but the transverse harmonic waves are effected by all the obvious things (barrel stiffness, overall rifle weight, bullet weight and velocity, etc.) but they are also effected by the shooter and how the shooter resists the recoil. thus is why perfect follow through is needed. now obviously theres nothing wrong with watching the shot after the bullet leaves the barrel if your followthrough is good but if the shooter needs to take there eye out of line with the sight (out of the field of view of the scope, peep, irons) then something is really wrong with the shooters rifle, sighting or shooting technique.