Good video on tac reloads here. No empty mag-throwing pageantry just good fundamentals. My only question is why would anyone ever train to reload using the first method shown in each example?
It seems to me that a tactical reload – i.e. one where your mag is not yet empty- would be the time where you would want to bring that fresh mag up to the one you're about to remove. It doesn't make sense to me to leave the gun limited to the chambered round for that extra time- even during a lull in the action. The economy of motion should result in a faster mag change too.