Hmm...
I love Open Range, but in the final scene Kevin Costner fires his trusty six-gun about 3-4 times, and then without reloading fans it about another 8-10 times into the same baddie. On the commentary he admits that it's hokie but says it was just too much fun to fan the gun that much. Lame.
Later a shot from a shotgun flings a guy about 8 feet through the air and slams him into a building. Anyone heard of Isaac Newton?
Rest of the movie was pretty cool though, and you can tell they ain't firing squib loads. That part I liked.
Worst overall movie? The recent Assault on Precinct 13 was disappointing, although I can't point to any specific scene. I may have to vote for Commando, as some others did. The scene where 5-7 baddies come running across a lawn the size of a football field and Arnold mows 'em down with machine gun fire is pretty sad. Can't help liking Arnold, though.
OK..I've got it. Mission Impossible II. That was about the only movie I've ever watched where the action got so ridiculous that I was unable to follow it even for the sake of staying with the story. Worst scene: Tom Cruise skids a motorbike at high speed, on the front wheel only, holding the bike with his left hand, while executing a 180 turn (still on just the front wheel), while with his right hand he empties his pistol about as fast as you can humanly fire it and takes out 2 or 3 tires on a moving, skidding car that's 20-30 yards away. That was the point where I gave up even trying to hang in there. The final fight scene might win the award for the Most Ridiculous and Implausible Fight Scene Ever, in my book. The whole movie was filmed by people who have never fired a real firearm at a real target, IMHO.