An interesting article at Cracked.com debunks some modern misperceptions that the public has about guns:
#5. Silencers Turn Gunfire Into a Gentle Whisper ("An unsilenced gunshot is around 140 to 160 decibels... A silencer can get that all the way down to 120 or 130 decibles, aka the sound of a jackhammer.")
#4. Machine Guns are Magical Death Machines ("Because you can't actually see the bullets in a machine gun, Hollywood takes this as a blank check to treat the inside of a gun as a magical bullet factory.")
#3. Bulletproof Vests Are Magical Force Fields ("In movies, body armor (made from a material called Kevlar) turns most guns from magical death-wands to hilariously overbuilt Airsoft rifles.")
#2. Gratuitous Cocking ("That "click" is the sound of a hammer being cocked back, and movies seem to be saying, "This means the gun is ready to fire now, baby!" It doesn't mean that, however. It doesn't mean anything. The gun was already good to go.")
#1. Bullets Explode Everything ("In the movies, bullets and anything mildly flammable have a matter/anti-matter relationship. The second hot lead touches a car's gas tank, it and everyone inside are going up in flames.")
More details at the link.