Practise is definitely important but to know for sure where your bullet will strike at 300 yards you must actually shoot the gun and load at 300 yards.If you never do that you are merely guessing at your trajectory.Trajectory tables are a guide but are often not that accurate at the longer distances and even moreso if you don' t chronograph your loads to determine the exact velocity that your load produces in your gun.Velocities printed in manuals can vary a great deal from the actual velocities that your gun produces.