From Nordic Larp Wiki
Blank-firing firearms are used to simulate gunfire in a larp. Blanks are cartridges that do not fire bullets, but still have the loud bang and flash. Various types can be used in regular firearms or in specialized blank-firing weapons such as starter pistols or weapons designed for theatre or movie use.
While blank-firing firearms have a high degree of realism, that does come with several serious dangers:
Using blanks often requires special licences permission from the authorities and can easily be mistaken for actual gunfire by outsiders, who might become worried if not warned beforehand.
While blanks do not fire an actual bullet, they are still actual firearms that expel fire and paper fragments and should not be fired directly at people or in close range as they can cause burns or even penetrating wounds. Extreme care should be used at all times when using any firearm.