Blank-firing adaptor

A blank-firing adapter or blank-firing attachment (BFA), sometimes called a blank adapter or blank attachment, is a device used in conjunction with blank ammunition. Blank firing adapters are required for allowing blanks to cycle most automatic firearms. It can also be a safety feature designed so if a live round is mistakenly fired, most of the energy is spent smashing through the BFA reducing both the range and damage inflicted. A BFA may also divert the hot gases from a blank discharge out to the sides, reducing the risk of injury to the target of an aimed shot.

The design of the blank firing adapter depends on the intended use. Different designs are used for different firearm actions and different user needs. For military use, BFAs are made obvious in order that they can be seen to be fitted - in addition to its role in cycling the action of a weapon, the BFA also prevents debris from the blank round (and in some cases, inadvertently loaded live rounds) escaping. This debris could cause injury to nearby personnel if the BFA has not been fitted or has fallen off. Use in motion picture special effects, however, requires the BFA to be hidden from casual view, so as not to disturb the illusion of live ammunition being fired, a feat usually accomplished with replacement barrels, the diameter of which is significantly reduced just in front of the chamber.

BFAs for blowback and gas-operated firearms are relatively simple. These weapons depend on high pressures in the chamber generated by the combustion of the propellant to push the breech block to the rear, allowing another round to be chambered and fired. If a blank round is used, there is no bullet to seal the barrel, and the combustion gases exit through the muzzle without building up enough pressure to rechamber the next round.

Simple BFAs for these firearms consist of a metal plug with screw threads. The adapter is attached to the muzzle of the firearm, and may attach to or replace the muzzle brake if there is one. A means is provided to allow some of the powder gases to escape. This can be adjustable, allowing it to regulate the amount of pressure used to rechamber the next round.

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