How feasable and/or effective would it be to eject an empty handgun magazine and kick it (accuratley) towards an opponent from mid-fall during a close quarters fight (say a melee attacker rushing down a corridor towards the kicker)?
No, and no.
So, first thing is that, depending on the handgun, the magazine may not drop freely. This is a preference feature. Some people prefer to release the magazine and pull it free, while others prefer to allow the magazine to drop freely into their hand when ejected. There isn’t really a, “better,” option here. Both positions come down to what the user finds more intuitive and comfortable.
If you’re wondering, this isn’t something that’s likely to trip up an experienced shooter. Anyone who’s spent time on a variety of firearms should be able to adapt to the gun they’re handling. You can also tell if the magazine will drop away when you load a magazine; based on the amount of friction experienced.
Even with a pistol where the magazine can drop freely, you’re not going to want to literally drop the magazine on the floor, or kick it. Handgun magazines are expensive; Depending on the model of handgun, those could cost anywhere from $10 to over $100 (on some rarer pistols). (I was specifically looking at a Bren Ten magazine for the upper end of the spectrum, if anyone’s wondering.) If anyone’s thinking back to the Desert Eagle post from a couple months ago, those magazines will set you back a little under $50 each. You do not use these once and discard them.
You also don’t, usually, want to eject empty magazines. Much like your car, you never want to run a gun dry. While it’s fairly easy, in a controlled situation, or on a range to keep track of how many times you’ve fired, and to know the exact state of your weapon; this is much more difficult in a real firefight.
You reload when you think you might be getting low, or when you’ve got time and ammo to spare, you put the partial magazine in a different pocket from your fresh mags, and replace it with a fresh one. The last place you ever want to be is in a situation like the one you just described: staring at someone who wants to kill you with an empty gun in your hand.
Fresh mags are heavy. That is to say, depending on the gun, a fully loaded magazine can easily weigh more than a pound. Most of that weight comes from the loaded rounds; the magazine itself is just a thin plastic or metal shell to hold and feed them into the firearm. They’re really not designed to take much abuse, and depending on the magazine, may be somewhat fragile.
Under controlled circumstances, kicking a falling object is something that a practiced martial artist should be able to do easily. Putting it in the rough vicinity of where they want it is also quite doable. Being able to do either of these things in an actual combat situation, not so much.
This is the kind of stunt you’d expect to see in a John Woo film, (I’d be slightly surprised if he hasn’t done some variation of this), and I know I’ve seen it on film before, somewhere. It’s in that range of slightly ludicrous that plays well when you’re working with characters that are (at least) slightly superhuman. But, if you’re dealing with normal, mortal, characters, this is neither feasible nor effective.