Cool, thanks for responding :)
you'll see him tossing weapons, magazines, and even his rack-mount flashlight onto the floor as he goes along. There is a second or three in which the hallway is not visible, as he's turning to shoot into a side room off the entry hall, and it's during that time that you can hear a sound very much like a magazine hitting the floor a few feet away.
When he does drop things, you see it happen, and he doesn't throw them - especially not 10+ feet. With volume up, I can hear the sound you're probably referring to, but it also sounds very much like a door opening or closing, somebody tripping on clutter as they scramble away, a switch on the gun being flicked, and so on.
His hands appear to be on the weapon during the fraction of a second he could be throwing a magazine down the hallway - he doesn't seem to have opportunity. He also doesn't have any motive for doing what you suggest. Everything else he did seemed pre-planned and very efficient.
And why did he briefly pause to inspect the magazine as he passed it, if he had just thrown it there under 2 seconds ago?
You mention Occam's Razor, is your explanation all that likely? Many intelligent rational people I respect favour another explanation, which is that once again elite forces within governments are exploiting people for societal change that favours them, like disarming the populace and increased surveillance powers.
Perhaps investigators will (or have) questioned the shooter about that clip? I'm sure they've been going over the footage nonstop since it happened, and they have many eyes, so they're aware of it at least.