Not-So-Fake Prop Weapon

A Murder Mystery trope.

The victim and the attacker are both actors, rehearsing or acting out a scene with a prop weapon. Unbeknownst to either, a third party has switched out the prop weapon for a real weapon, and the attacker kills the victim before realizing the switch.

For the Real Life version of this, please see Fatal Method Acting.

Comic Books

 * In The Maze Agency story "The Death of Justice Girl", the actress playing Justice Girl is killed when the murderer swaps out a pistol loaded with blanks for one loaded with live ammo.

Film

 * The Man Who Knew Too Little has Bill Murray's character firing what he thinks is a prop gun.
 * In The Clones of Bruce Lee, the gold-smuggling director's yes-man suggests using this to kill the Bruce Lee Clone they suspect to be a secret agent. As Spoony pointed out in his review, this is very badly Harsher in Hindsight, since Bruce's son Brandon was killed on the set of The Crow by a weapons malfunction.
 * Happens in the Elvis Presley film Frankie & Johnny with a prop gun that's been loaded with real bullets.
 * In Shaun of the Dead, not only is the rifle displayed at the Winchester pub real, it's also loaded.
 * In The Prestige, Borden emphasizes that a bullet-catching trick where the (bulletless) gun is fired by an audience member is still dangerous, because the volunteer can slip something down the barrel and fire it for real. Guess what happens.

Literature

 * The Polish book Dwie "Kobry". A character in a TV show is supposed to be killed by a faulty electrical socket, but the socket turns out to be a real one and the actor is actually electrocuted.
 * The initial murder in Witness in Death is accomplished in this manner during a stage production of Witness for The Prosecution.
 * Caroline Graham's novel Death of a Hollow Man has the actor playing Salieri in a performance of Amadeus fatally injured when someone removes the protective tape from the blade of the prop razor that the character cuts his throat with. This stayed the same when the story was adapted into an episode of the Midsomer Murders TV show.
 * Ngaio Marsh's novel Enter A Murderer has a prop gun used for an on-stage killing loaded without the actors' knowledge.
 * Ngaio Marsh's novel Swing Brother Swing uses a sneaky variation of this. It's suggested that a musician was murdered during an on-stage gangster routine by a dart, not a bullet, being loaded into a blank-firing pistol. But actually.
 * Happens in the Joanne Fluke/Hannah Swenson mystery Cherry Cheesecake Murder, when the director of a movie shoots himself with a supposed-to-be-not-loaded prop gun, to attempt to demonstrate the emotion required in the scene to the actors.
 * Inverted in Wyrd Sisters, when the Duke loses his mind and begins stabbing people, including himself, with a prop knife. No one is hurt, but he's convinced that everyone he strikes is dead, and even insists he's now a ghost to Death himself.

Live-Action TV

 * Psych has used this plot, during a telenovela episode. Until Shawn is able to prove otherwise, everyone is convinced that the actor with the knife was obviously completely responsible (and dumb enough to stab someone in the chest on live television). In true Psych fashion, proving his hypothesis almost resulted in Shawn's own death by not-fake prop weapon, this time a nail gun.
 * Monk also did it. The weapon was switched . The actress accused of murder rightly points out that she would have been able to feel the difference in weight and balance between the prop knife and the real one.
 * Done in Oz during the prison production of Macbeth, though with a shank.
 * Midsomer Murders:
 * Happens in the episode "Death of a Hollow Man".
 * And in "The Magician's Nephew". the spikes inside a illusionist's 'Cabinet of Death' are coated with a fast acting poison.
 * Black Adder: The Black Adder tries this one, but changes his mind when he learns the victim has information he thinks can prove . The information ends up.
 * An episode of The Professionals centered around a gun used in a crime being dumped in the prop bin of a theater company.
 * Diagnosis Murder featured a morning show staging a shooting between the hosts as a publicity stunt. Someone switched the real bullets for blanks and the cohost gets shot.
 * Ellery Queen: A movie is being filmed based on Ellery and the man playing Ellery is killed by a gun that was supposed to be filled with blanks.
 * Castle had two variants:
 * While the two guns used by the victim and the "murderer" were both real, they were so wildly inaccurate (as a disgruntled cop and a laser sight would attest) that there was no chance of one party hitting the other. The third party hid in a tree nearby.
 * And another one earlier in the series, also with a real gun but the shooter didn´t know there was a bullet in the barrel.
 * An episode of Bonanza has Hoss get framed for murder when the blank rounds from a prop gun get switched for real bullets and the blanks turn up in his saddle bag.
 * A Smallville episode had someone put live ammo into a gun that was going to used to "shoot" the lead actress in a movie filmed in the town. The would-be murderer learned about Clark's powers when he somehow saw him catch the bullet.
 * One One Thousand Ways to Die clip has a magician killed this way while performing the bullet catch illusion.

Professional Wrestling

 * The Honky Tonk Man almost killed Jake Roberts when the prop guy got a real guitar instead of a prop.

Real Life

 * A Real Life tragedy without the malice. On October 12, 1984, actor Jon-Erik Hexum was filming a scene for the CBS TV series Cover Up. In the scene, he had a .44 magnum revolver loaded with blanks. After several takes, filming of the scene was delayed. As the cast and crew became more annoyed, Hexum decided to relieve the tension by performing a little joke. He grabbed the prop gun, put it to his temple and squeezed off a round. (People on the set later said that they believed that Hexum had assumed that the prop master had unloaded the gun between takes.) The blank -- which was made up of a standard bullet casing and a standard powder charge, but with a "projectile" that had the consistency of a piece of blackboard chalk -- crushed Hexum's temple. The blunt-force trauma was similar to that of being hit by a baseball bat swung by the hardest-hitting Major League-level home run slugger. Six days later, the 26-year-old actor was declared brain dead and, following to the wishes of his mother, his organs were harvested for transplant.
 * Bruce Lee's son, Brandon Lee died during the shooting of The Crow, when he was shot with a real gun. The gun was supposed to be loaded with a blank, however a real bullet ended up in the barrel.

Video Games

 * In Hitman: Blood Money, Agent 47 has the option of switching a prop World War I pistol for a genuine one in working condition to kill a target, who is to be executed in the play Tosca.
 * Subverted in the first Phoenix Wright game, done to distract the player. The victim is killed with a large prop used for the TV show he co-starred in. Phoenix tries to argue that if it's a prop, it shouldn't have worked, but we realize that the blade itself is actually reasonably sharp. Subverted further in that
 * A case in a CSI game involves an actress being killed on stage, supposedly by a prop gun. However, there are several inconsistencies: the man in charge of all props made the bullets and loaded them himself; the actress firing the prop weapon never actually pointed at the murder victim. It turns out the killer was the dead woman's husband, who found out that she was having an affair with the other actress. He fired a rifle from a balcony at the moment the prop gun was to go off.

Web Comics

 * Inversion: In The Adventures of Dr. McNinja, Gordito's father is killed during his gunslinger circus act because  sabotaged his guns before the performance.
 * Had the  assassin UNLOADED Gordito's father's guns, the veteran shooter would have noticed the weight difference and presumably halted the act or loaded them. He sabotaged the guns so they were fully loaded, but incapable of discharging.
 * Wait, the PETA sabotage was only discovered after Dr. McNinja had taken in Gordito, wouldn't Gordito have noticed the sabotage when the guns were given to him?