Glocks have hammers, and can be cocked without racking the slide.
When you forget to take the safety off, you can still pull the trigger, but the gun just goes 'click' and doesn't fire...
The military has captured replicator technology from an alien crash site, and applied it to M-60 feed trays... Thus, the belt GROWS BACK into the tray as you fire the weapon..
After chasing down your target, allways corner them, get stuck in a stand-off, and then finally (while threatening to shoot eachother) chamber a round and/or cock your weapon. The other guy is allways an absolute idiot, and doesn't take this oppertunity to blow you away (or forgot to load up before he encountered you, and is doing the same thing you are)...
Land mines only go 'boom' if you step on them and then take your foot off. The concept of a mine that explodes immediately upon being stepped on is 'not possible'...
When defusing a 'simple' bomb (a stick-in detonator/cap inserted into a brick of plastique with 2 wires and a timer), the simple step of PULLING THE FUSE OUT OF THE EXPLOSIVES.
Repeat after me: 'there is no recoil'
9mm can penetrate a car's body and puncture the gas tank...
Getting shot with a bullet proof vest knocks you flat, and you must stay flat untill someone pulls the slug out of your vest, at which point you are back to 100%.
Bullet wounds to extremities and non-vital areas are harmless...
You can fire (on full auto, with no jams) blanks and real ammo from the same MP5 just by changing mags.
'Jungle taping/clamping' mags allows you to fire 60 rounds from 2 30rd mags without removing and inverting the mag...
All bullets (incl 9mm and .380) are incinedrary. If anything flammable gets shot, it's a 4-alarm event...
Cars come fresh from the factory with a tank of nitroglycerine in the trunk. Even the slightest fender-bender causes an explosion to rival a hellfire (or Movie-brand RPG) hit...
Rocket launchers fire rounds with the destructive power of a helicopter-launched antitank weapon.
Unguided LAWS rockets can 'lock on' to the 'heat signature' of a guy lighting up for a smoke in the rafters.
There exist 9mm rounds that when fired from a MAC-10 can penetrate the blade of a bulldozer. These rounds are loaded with bullets that look like the tip of a sharpened pencil, and are pinpoint accurate (despite there being no surface available to engage the pistol's rifling when fired)...
Stormtrooper Syndrome: NO ONE CAN HIT SH*T WITH ANY WEAPON, UNTILL THE 'CRUCIAL SCENE'. At this point, shooter, range and weapon do not matter, as whoever is supposed to 'make the shot' will...
Grenade launchers are 'super shotguns' to be fired at targets point blank, and aimed through rifle (not ladder) sights...
People build super-expensive, impenatrable secure or secret rooms, stock them with all manner of emergency gear, and hide the 'secret documents' or big stash of cash in there, but no weapons (not even an old rusty pump shotgun). ('Panic Room'. The whole movie could have ended right at the start if the 'secret room' had just ONE shotgun with a full tube)...
When the obvious solution to a problem is 'JUST SHOOT THE !#%!#%!#%', you have to try some other means of resolution (such as running away or screaming for help...
In the case of animal attack, burglar, or similar scenes, NO ONE ever has a gun. But get to that 'crucial' point, and the main character can shoot like a champ...