A lot of the early Western TV shows and movies were notorious for having magical six-shooters that would shoot 8 or 9 bullets without reloading.
Jurassic Park
The two kids and the two Paleontologists are in the computer room and the little girl has just gotten the park (semi) back online. Sam Neil is holding a shotgun in his hand. While on the phone to Richard Attenborough he fire four times. (from a shotgun) Cut to the thing he shot at and there are four distinct bullet holes.
The worst is when someone hit by an arrow does that flying-backwards thing.
Maybe he was shooting slugs? (I don’t remember the scene in question) Regardless, I’d rather be using slugs than buckshot on a critter of unknown toughness and thick composition, like a grizzly bear.
Except for the automatic whose hammer goes up and down in between shots. (During the parking lot scene where John realizes he has total control of the Terminator, and the two beefy guys try to intervene.)
Not a usage issue, but pretty stupid nonetheless.
Maybe it was a Magnum arrow. 
I don’t recall the scene well enough to recall the size of the impacts (or if it was previously established he was loaded with buckshot), but if he was firing slugs you’d only expect one impact per time he fired.
Little shop of Horrors (Rick Moranis version)
Seymour’s SIX SHOT snubnose revolver holds at least 19 rounds, and no, there is no loose ammo lying around or speedloaders…
Numerous revolvers with silencers.
I’ve read that the actor did that on purpose, as a kind of subtle sneer at the director.
There’s a Clint Eastwood western – not a bad movie, to be sure – where every single damn gunshot uses exactly the same sound effect, right down to the whistling ricochet sound. Over and over and over. Agonizing to listen to. The Foley guy should be…spanked.
Well, it’s fudging it a bit, as it’s (typically) not a personal weapon, but…nukes.
Almost always detonating at ground level—even when air-delivered, and an airburst would actually greatly aid the bomb’s destructive power—and, of course, producing a mushroom cloud. Not forming a mushroom cloud, from the effects of the blast and local atmospheric conditions, mind you. The cloud often simply appears, fully formed, as if it were merely summoned. Possibly by the Atomic Genie*.
*(No, not that one.)
Which sounds exactly like “wack!” each time.
No talk of slugs. The holes are too small for shotgun slugs. (they look like holes a .22 or maybe a .38 would make)
They were all Nagants. 
Yeah, slugs was, in all honesty, a bit of reach. I don’t recall any movies where shotguns aren’t firing buckshot.
Hey, I’ve got one of those. But my suppressors are too small for that bullet to pass.
While he may have flinched, how he uses the trigger is not the main problem or cause. That wouldn’t make him an Instant Marksman. I hate all these “one trick” types of tropes. Such as “trouble hitting the target? Just breathe out as you squeeze. Now you can hit anything!” Zombieland is the first one that comes to mind, but there are others.
I could expect a lowered hammer to be an offscreen decock. But I know better than that to assume!
Honorable mention: Ash’s (Evil Dead) double barrel shotgun always has at least 3 rounds. Doesn’t count as that’s intentional. Also anything where excessive cocking is done for effect. like one Simpsons episode.
Terrible trigger control makes me uncomfortable.
Snap caps. You can make do with a dummy bullet or other things, but this is safer for rimfire.
Kill Bill (the second one?), rock salt shells. Which by the way, doesn’t work.
His shells had four BBs in them, and he is such a good shot each one went to the same place? And of course he loaded them all exactly the same.
Semi and full auto firearms need to be modified to fire blanks. If they aren’t, often you’re going to have to manually work the bolt/slide after each shot. To fire 21 gun salutes, the Honor Guard had to attach Blank Firing Adaptors (BFAs) to M-1 Garands, M-14s, and M-16s.
Even if you’re not talking about For A Few Dollars More, you’ll still really enjoy this scene.
Especially the end of the clip - admittedly I don’t know much about guns, but I’m having trouble figuring out why shooting a hat in mid-air would make that exact same noise every time, like it ricocheted off…something metallic…in the middle of the sky. 