Thanks to the relatively slow and incomplete combustion of black powder. A similar spectacle happens when vastly overpowered rounds are shot out of very short-barreled guns such as pistols. The following is S3E5 of “Bones” and she’s shooting a S&W 500 that only has a 4-inch barrel, in dim light:
ETA: and her arm is angled toward the camera at about a 45-degree angle; the fireball would be even longer if we saw it fully from the side.
I meant a prop gun with no rounds of any sort in it - I’m guessing the sound was spliced in afterwards. I don’t recall if there was any visual sign of the gun going off (eg smoke, recoil) shown.
Back in the '90s, on a beautiful spring morning, I had just gotten out of the shower when I heard a gunshot outside my apartment block in Moscow.
Now, my apartment was on the 16th floor of a high-rise in a ring of buildings around 400 feet in diameter. (Think of the saucer section of the original USS Enterprise.)
The window was wide open, and I didn’t want to go anywhere near it because it sounded like the gun was fired right outside my kitchen. As it turned out, the cops showed up on the far side of the ring, so I assume that what went down happened there.
My point is, that shot was LOUD! LOUD, LOUD, LOUD! I’ve fired military-grade pistols and rifles, and I’ve never heard a sound like that anywhere else.
Speaking of blanks this is something I’ve read a few times usually in bad pulp novels and not actually seen in movies/TV.
But the idea of having your home defense gun or even personal firearm first round be a blank, followed by actual rounds.
The “justification” is that if somebody you don’t know gets ahold of your gun, you know you have a brief window to charge or disarm the person with your gun because the first round won’t hurt you. Then with blank out of the way you can then use real rounds back on the person who took your gun.
What if they just keep squeezing the trigger when they see you weren’t hit the first time? 
How was it done on Broadway? Because the movie scene has the camera in the perfect place: right in front of the face of the guy who has a gun pointing at the back of his head. And, from that perspective, the guy with the gun doesn’t need to fire a blank or even pull a trigger; at the exact moment when there’s a BANG, the audience can’t actually see the gun (or even the gunman, such that no recoil or whatever needs to be shown lining up with the sound) — which, as far as I can tell, means it doesn’t need to be “a prop gun loaded with blanks”; it only needs to be “a prop”.
In the movie there was definitely the sound of the gun discharging and the smoke from it. I have no doubt that real gun with a blank was used (this being in 1972, well before the famous cases of people being killed by being shot at close range with blanks). But I note that you can set up a (camera) shot so that it appears that the gun is close to someone’s head and in line with it, but actually not be.
I know that they used a gun with blanks when I saw it onstage.
Did anyone in real life ever encounter a portrait with the eyes cut out and replaced by the real eyes of a person watching from behind the wall?
Here’s the scene from the film Sleuth – the gun is clearly behind the mask (presumably with a head i it), and you can see the smoke from the shot
It’s all the way at the end of the excerpt. But it’d be perverse to think they didn’t actually shoot a blank back in 1972, and that someone’s head (a stuntman, perhaps) was inside the mask.
On the Broadway stage it was similarly staged – there’s a two-story set with a winding staircase in the middle (much as in the film). A in the film, Milo is shot at the top of the staircase and slides dramatically partway down.
You don’t need an elaborate set for the play. I saw an amateur production that was on a set with no staircase at all. The gun was a cap gun, not a stage gun with blanks. So Milo couldn’t have been injured by it.
You could always load the gun with soot, à la Smiles of a Summer Night.
I’m not sure about the stage, but I’m almost certain there’s no blank fired in that scene. There’s no disturbance of the air or the mask when you hear the gun go off, and the smoke is just drifting as if it came from a cigarette. All you really need to produce that is to have someone provide a wisp of smoke before the actor moves their head down.
And with a secret passageway.
Maybe they there are a lot, but we don’t see them.
Secret passageways were a real thing in old mansions. They gave the servants easy access to rooms when the aristocrats were gone, and enabled the servants to disappear before the aristocrats entered the room. They usually led to storerooms and laundry rooms, rather than to a mad scientist’s lair.
Usually.
A couple of examples:
Jon-Erik Hexums fatal joke
Tucker Thayer - High School Production of Oklahoma!
Both of those from blank pistols. Brandon Lee was killed because a bullet was lodged in the barrel ahead of a blank round.
The concussion from blank rounds, and the wadding that normally holds the powder in, can be very dangerous. Just think of powder=driven fasteners, using blanks to drive pins in wood, concrete, steel, I used the low power ones in my blank pistols while training and running bird dogs, and you could feel it if you held it within about 8" of your leg when you fired it off.
Obviously, just like fireworks, blanks can be dangerous if used irresponsibly. However, unlike the 30,000 (or whatever) gun related deaths every year, when it comes to blanks people mention the same two or three blank related deaths that made the news over the last few decades.
Unless there are vast numbers of blank related deaths (or even injuries) that don’t make the news, I think it does fit for the second half of this thread title “almost never happens”. Yes, they occur, and yes, they are tragedies when they do, but a bunch of whataboutism pasted from any GD or pit gun debate.
To me, it seems ridiculous to think that just because the script says the gun is loaded with some blanks and some live rounds that the prop gun is actually loaded with anything at all (other than dummy rounds to fill the cylinder, perhaps). That’s just how movies and theater works. Peter Pan can’t really fly, either.
Well, of course you don’t see them- they are secret passageways. 
No. The scene goes like this:
It’s literally one frame filled with clown, and the next frame smoking gun. There is no shot actually seen to be fired close to MC’s head. LO didn’t even need to fire the gun, the sound was (presumably) dubbed in afterwards.
Very few people use blanks as opposed to live ammunition. Off the top of my head Hollywood, sports events, dog training, construction. A very small part of the overall population, so of course the numbers for live ammo vs. blanks will be much different. People hear “blanks” and tend to assume “safe”. Not the case at all.
Blanks for shooting tennis balls from your SKS or Garand grenade launcher.