How movie sets hide the fact that they’re firing blanks in films
Troops are very acquainted with using blank rounds. We slap in a magazine filled with them, screw on a blank-firing adapter (or BFA), and continue training for the day. Without fail, we go out and someone inevitably takes a photo of themselves trying to look all badass like in the movies — but they can't. That BFA just looks ridiculous and lets everyone know immediately that they're just training.
So if you really want to look as badass as they do in the movies, you have to look at how the special effects teams on a film set do it. They're obviously not firing actual, live rounds at each other during the film's climactic ending — that'd violate so many safety regulations and break countless union rules — but to us, the audience, it feels real.
They're firing firing blanks, just like the troops in training, but they've some ingenious ways of hiding that fact.
When you put the flash hider back on, you can't tell the difference unless you're up close and personal.
(Combat Disabled Veteran's Surplus)
Most semi-automatic firearms use the gas expelled from ejected rounds to cycle in another round. Blank rounds don't create enough gas pressure in the barrel to make this happen, so, if you're firing blanks, you need a blank-firing adapter. Firing without a BFA will inevitably cause a failure-to-feed.
The BFA acts more as a plug for the gas. It keeps in just enough gas to build the pressure needed in the chamber for a person to continue shooting without interruption while still letting enough oxygen in.
On a film set, however, you can't have the actors looking like they're troops in basic (unless that's what the film is about). Instead, they screw a tiny blank-firing adapter onto the end of the barrel, underneath the flash hider, as shown below.
If you love 'Sons of Anarchy'... just don't hit pause during the gunfights of the first season. Yikes.
Other film sets use entirely decommissioned firearms that have been repurposed as production weapons. Propsmasters will replace most of the assembly with components that require less gas pressure to function. These are close copies, but, ultimately, they're just replicas — and enthusiasts can tell.
People who've been around firearms can quickly spot when filmmakers add an abundance of flash coming out of the muzzle. But it's a known inaccuracy and it's done with a purpose. Films, in general, are shown (and often captured) at a rate of 24 frames per second. Without enhancing the muzzle flash, there's a good chance that the camera won't capture a flash at all — and that visual bang is an important part of selling the illusion of real gunfire.
But then there are the films crews that skip all of these mechanical steps and add the flashes and sound effects entirely in post-production. It's comparatively cheaper when you factor in the costs of safety crews and whatnot, but the results aren't always so great...
An interesting and positive side note: Lee's stunt double, who'd also replace him for the rest of the film was Chad Stahelski, the man who'd later direct John Wick.
Which leads us to the elephant in the room — the incident that took place on the set of 1994's The Crow, which lead to the death of the actor Brandon Lee. One of the special effects guys tried to save time and money by making their own blank rounds from live .44 rounds. The weapon they were using on set was an actual handgun and made use these modified rounds. Well, one day, it didn't work perfectly and a piece of the cartridge broke off and got lodged in the barrel. No one bothered to inspect the firearm or clean it. They tossed it aside and carried on with production.
A few days later, when they needed more firearms for a bigger scene, they grabbed that same handgun. Loaded with another home-made blank and with that fragment of the cartridge still in the barrel, a stunt actor fired it at Lee. Since his character was supposed to react to the shot (and Lee was known for being a gifted actor) no one noticed that Lee had actually been shot until well after the camera stopped rolling.
Though nothing can undo the tragedy that befell Brandon Lee, the silver lining is that firearms have since been treated with more care on set. Many safety regulations are now in place to prevent such a horrible tragedy from happening again.