Blank ammunition

A blank is a type of cartridge for a firearm that contains gunpowder but no bullet or shot. Blanks use paper or plastic wadding to seal gunpowder into the cartridge. When fired, the blank makes a flash and an explosive sound (report), the wadding is propelled from the barrel of the gun, and the firearm's action cycles. Blanks are often used for simulation (such as in historical reenactments, theatre and movie special effects), training, for signaling (see starting pistol), and cowboy mounted shooting. Blank cartridges differ from dummy cartridges, which are used for training or function testing firearms; these contain no primer or gunpowder, and are inert.

Specialized blank cartridges are also used for their propellant force in fields as varied as construction, shooting sports, and fishing and general fun.

Blanks are commonly used when the sound and flash of gunfire is needed, but a projectile would not be safe, such as in military training maneuvers or funeral honors, in movies that require gun fights, in starter pistols to signal the beginning of races and in the equestrian sport of cowboy mounted shooting.

For military applications, blanks are typically used with a special blank-firing adaptor in the firearm that constricts the barrel, keeping chamber pressures from the blank high enough and for long enough of a duration to cycle the firearm's action. In the case of non-crimped blanks, it also serves to pulverise the plug to prevent it leaving as a projectile.

...
Wikipedia