Major characters never run out of ammunition, nor do they ever have to reload. (If the movie does make them reload, they never have to actually carry any spare ammo until that scene)
Guns never run out of ammunition unless escape would be otherwise impossible. The first shot or burst of fire from a bad guy always misses, and is there just to announce that a fight will be taking place.
Bad-guy hand grenades make noise and smoke, but no real damage; good-guy hand grenades are devastating but selective; they will destroy tanks, but won't hurt the thrower, even if he drops one on his toe.
Bad-guy grenades used by good guys become good-guy grenades, and vice versa.
When the villain runs out of bullets, he'll throw away his gun. When the hero does so, he'll conveniently come across another.
Machine guns submerged underwater for a long time won't jam or misfire when the hero pops up to use them. (see any Rambo movie)
A cigarette case/lighter in the shirt pocket will always block the bullet.
When the hero faces a ridiculously large number of shooters with high powered weapons, they will all miss after several shots. Then, the hero will pulls out this gun that looks like a toy and start picking off the bad guys from half a mile away, usually hitting them in the forehead.
People always pump out a few (probably used) shotgun shells at each corner when chasing someone.
When people aim a rifle with binocular-sight at someone on a very long distance, they manage to keep them in the bull's-eye all the time even if they move around.
When faced with dozens of armed opponents, the good guy will show up and appear to be shot, perhaps dozens of times. He will fall down, and presumably be dead, but will later miraculously turn out to have had the foresight to wear a bulletproof vest, armor plating, or even a silver tray to protect his torso (Batman). No one will ever shoot him in the head, where he is unprotected. Afterwards, instead of learning from his extremely good fortune, he throws his protection away, confident that the same situation cannot recur in his movie.
When superheroes like Batman or Robocop use high technology to protect themselves, the bad guys never take advantage of obvious weaknesses, such as no face protection.
Characters shot with guns will fly backward, or upward and backward, through the air - the laws of physics notwithstanding.
Characters use silencers on revolvers... and it works.
In 50% of action movies made after 1988, "Teflon Coated Cop Killer Bullets" will be referred to.
No movie character will ever use or refer to a safety on any firearm.
No movie character will ever use a .22-caliber weapon.
The cowboy who exchanges a dozen shots with the bad guys without hitting one will nevertheless be able to hit and detonate a stick of dynamite from 150 feet away with a revolver on the first try.
Once a character has flipped up the long range site on his rifle, he will always make his next shot.
Bullets removed from shooting victims and displayed to the camera will not be misshapen in any way from the impact - and will sometimes still have the casing attached.
Shots fired at the rear of a vehicle will cause the gas tank to explode.
Shots fired at windshields never deflect; they always penetrate and hit the bad guy in the forehead. If the good guy is driving, he'll simply have to duck a little to avoid them.
Shots fired at guys hiding around corners never whiz past; they always strike the edge of the building near the character's face.
Shots fired in Westerns that do not hit a character always ricochet loudly.
If there is a trough of water present in a Western Gunfight scene, at least one shot will splash spectacularly in the water.
Western characters are never shot in the legs while hiding behind wagons.
No gun will ever jam or misfire after a quick-draw.
In a duel or in a gunfight between two characters standing in a street, at least one charcter is always hit on the first exchange of gunfire.
No debris will ever fall from a ceiling after a gun is Fired upward into it. Shurrikens and thrown knives never miss, unless they pin a character's clothing to a wall or tree.
Horses are never wounded in horseback gunfights.
Assassins will always wait 'till the very last moment to assemble their complex sniper weapon (often a pistol the size of a rifle).
Even weapons experts will freeze when confronted with a weapon which is not in firing condition-ie an un-cocked single actionrevolver or a submachine gun with its breech closed (also un-cocked). The personholding the gun must make several moves to fire the gun, and the adversary could just reach out and take the weapon, but the dropee just freezes even though often it is obvious that the cylinder is devoid of
Movie gunmen never lock and load their weapons when anticipating a life-or-death confrontation. Oh they have their weapons drawn, but not charged with a round in the chamber. They usually (always when carrying
a pump-action shotgun) wait until they confront their quarry to slam a round into the chamber with a dramatic ca-chunking noise.
Bullets, even though they are only pieces of lead-sometimes encased in copper, always make little explosions when they strike any kind of inanimate object.
Photos of loved ones, religous medals, and bibles can stop bullets better than a bullet proof vest.
All sub machine guns sound alike and have the same rate of fire
NEW requirement: all automatic pistols must be held sideways in order to be fired.
If you are a cowboy, aiming your rifle while using your horse as a support will always assure a first round hit.
All automatic weapons must be cocked in order to be fired, but bolt action weapons can fire two or three times without being cocked!
You can never un-jam a weapon by just pulling back the bolt and rechambering another round, 'though that will work 99 times out of 100 in real life.