Push/Pull is the preferred technique when loading/reloading a rifle.
With an open bolt, a magazine can be inserted and seated without any issues, normally.
With a closed bolt and a fully loaded 30-round magazine, seating the magazine can become difficult. This is why the magazines are usually downloaded 1-2 rounds to make the seating easier.
The push/pull technique is used to ensure the magazine is seated and locked in place. You do it every time you load a magazine, whether or not the bolt is open. You want a consistent method when reloading a rifle, not doing one method when the bolt is open and another when it is closed.
Never done the slapping part. I will assume it is done to ensure the magazine is seated.
Last edited by Steve in PA; December 15, 2012 at 09:10 PM.