How about the use of the 'shotgun slide sound efect' for just about everything gun related. Wether it's a bolt action, a pistol, a lever action, etc...
How about when the actors swing out the cylinders on their revolvers, then give it a spin. On TV it always makes a 'clicking' noise. Double actions don't click when the cylinder is in the loading position. I only had one revo that clicked when I turned the cylinder. That was a Super Blackhawk single action and the loading gate had to be open.
I was watching a COPS re-run. The female officer referred to the .44 Mag as the most powerfull handgun in the world. That may have been true in 1956 but not present day.
It's funny how they never had to reload those old cap-n-ball revolvers in the westerns. Those damn things never seem to run out of ammunition. I counted Clint Eastwood firing 32 times without reloading his old Colt blackpowder revolver.
Why is it that in most sniper movies, the scope's reticle has flashing lights, a computer screen, or some other type of non-tactical gadgetry. Remember 'SNIPER' with Tom Berringer. The spotter's scope had flashing colored squares on the sides of the reticle.
How about 'Surviving the Game', where Iced Tea sticks paper in the barrel and then lets the bad guy try shoot him in the back. Now, I know an obstructed barrel could cause a problem, but who would bet their life on it?
There are hundreds of others, I just gotta stop.