MythBusters did a similar test on whether the movie style knock-downs were accurate, using a variety of weapons on a human dummy made of ballistics gel. None of them caused anything even remotely resembling knocking someone across a room. (Edit: I did a google search, and the tests were done in episodes 25 and 38).

I can believe that the 7mm Rem. Mag could put deer down in its tracks, and that the deer then rolled halfway down a mountain due to the force of gravity, but, knocking a 200-300 lb animal halfway down a mountain? I'd really have to see it to believe it.

I'm also not knocking the 7mm Rem. Mag. It's a heckuva cartridge and I own one as well, and if I was on an elk hunt, I'd probably take it rather than my .30-06...