Even in gun-crazy America, most of us aren't shooting things as part of our day-to-day routine. So most Americans actually know very little about guns. Hollywood writers realized this a long time ago and, being writers, used it as an excuse to never do any fact-checking ever again.
Where You've Seen It:
In The Line Of Fire, Die Hard 2, No Country For Old Men, Shooter, practically every James Bond movie.
Cautious spies and assassins know that if you're going to take out a bad guy in an office or a library, be sure to use a silencer. It turns the concussive "bang" into a neutered "ptew."
Itty-bitty handguns aren't the only things you can silence. Giant freaking shotguns can even be fitted with a special silencer that renders them inaudible in quiet suburban neighborhoods.
Also, while silencers look all slick and expensive and fancy, Hollywood says pretty much any long, hollow tube will do the job. Grab a two-liter, stuff it with socks or something, and you can be just as dangerous as Mark Wahlberg in Shooter.
Exploding gunpowder is loud. Really loud. As loud as a jet engine. A little metal tube won't do a whole lot to stop that. This is what a suppressed handgun actually sounds like:
If you can't watch the video, let us sum it up: It still sounds like a freaking handgun. It does not make a soft phut that you could mistake for a kitten landing on a pillow.
An unsilenced gunshot is around 140 to 160 decibels--that's in the range where hearing it once can permanently damage your ears. If you've never had a gun go off next to you, trust us when we say it's loud enough that your whole body will flinch at the sound of it. A silencer can get that all the way down to 120 or 130 decibles, aka the sound of a jackhammer. Still loud enough to cause physical pain if it's close enough to you.
So a silencer really just makes a large gun sound like a smaller gun. If you're James Bond and are sneaking into the enemy's compound with a silenced pistol, you're basically hoping the guards will decide your gun is too small and wimpy to be a serious threat, and leave you be.
Many a GoldenEye guard made this mistake.
So why the hell do silencers even exist? Well, if you're in an outdoor, noisy environment, they can make quite a bit of difference. Specifically, they make it really hard to tell where exactly the shot is coming from, or how far away it is.
And as for silenced shotguns? They do exist. Here's one in action:
Yeah, that actually seemed to make it louder.
Where You've Seen It:
Starship Troopers, The Mummy, Max Payne, Commando, every John Woo movie, Scarface.
It's an old joke by now that nobody runs out of bullets in action movies (unless it's suddenly convenient to the plot, that is). Hollywood shows some restraint with revolvers--usually no more than 10 or 11 shots per six-shot cylinder--but damn, do they go hog-wild with anything that fires full-auto. So much so that that most of us have wound up with an utterly ridiculous concept of how those guns work. They're seriously depicting these things firing a hundred times more bullets than they can actually hold.
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. So in Commando we see Arnold fire without changing magazines for what seems like half the movie:
If you've watched a news broadcast about U.S. troops in Iraq, or played Modern Warfare, you've seen this gun:
That's an M4 Carbine. It holds 30 bullets. Here is a video of a small child firing one of those on full-auto:
He didn't give up after four seconds because he got tired. He was out of bullets. OK, how about the gun you always see the bad guys using, the AK-47?
Here's somebody firing a real one, full-auto:
Again, empty after four seconds. That's because fully-automatic weapons fire really goddamn fast--around 700 rounds a minute. Only you don't have 700 rounds in the gun, you have 30. So, do the math.
In fact, a U.S. infantryman only carries 210 rounds total, which means a battle conducted with full-auto machine gun fire would be over in less than a minute even if you count the time it takes to switch magazines. Fortunately, they fire on full-auto so rarely that many of the military's rifles don't even have that capability.
"But wait!" you say, "I've seen war footage from Vietnam and Iraq and everywhere else and you can totally hear machine fire chattering in the distance at all times. Somebody's using it, dammit!"
That's true, they're just not shooting people with it. Full-auto is only really used for suppression, that is, to make the bad guys duck their heads and hunker down while your people maneuver into position. In fact, virtually all bullets are used for this. For each insurgent killed in Iraq and Afghanistan, 250,000 shots are fired that hit absolutely nothing. About three tons of ammunition for every one dude killed. Picture Arnold lugging that shit around.
Somehow your best laid plans have gone awry, and now a bunch of Libyans in a Volkswagen van are out for your blood. They plan to shoot you repeatedly with their AK-47s, but you have an ace in the hole: a bulletproof vest.
In movies, body armor (made from a material called Kevlar) turns most guns from magical death-wands to hilariously overbuilt Airsoft rifles. A burst of fire from an AK-47 at point-blank range would turn most men's torsos into gooey paste suitable for spreading on crackers, but add a slab of Kevlar and you might as well have a Gandalf's magic protection bubble glowing around your torso.
"It's OK; protagonists never get shot in the head!"
In the real word, the vest that protected Back to the Future's Emmett Brown from the terrorists would only have been useful for its ability to keep all of his bits in one convenient (for the mortician) package. In fact, despite an additional 25 years of armor development, no body armor today would be able to protect Doc from that kind of assault.
The type of bulletproof vest you can actually conceal under your clothes provides exceptional protection against most handguns. But against an assault rifle like the terrorists were using up there? It's only slightly more effective than body paint and prayers to Khorne.
Prayers to Khorne and giant suits of armor synergize fairly well, though.
Our troops do have their own body armor, meant to protect against that sort of thing. It's much heavier and more rigid. But even it's only rated for effectiveness at further than 14 meters distance. When police wear body armor (45 percent do not) they don't tend to wear full military body armor. Probably because it weighs 33 freaking pounds and costs thousands of dollars. Since less than one percent of gun crimes involve military-style rifles, this is generally a pretty safe trade-off.