Blank-firing adaptor

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Troops in training using assault rifles fitted with bright yellow blank-firing adapters

A blank-firing adaptor or blank-firing attachment (BFA), sometimes called a blank adaptor 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.

The M2HB .50-caliber machine gun fitted with a blank-firing attachment.

1 Design
- 1.1 Gas operated and blowback firearms
- 1.2 Recoil operated firearms
2 External links

[edit] Design

The design of the blank firing adapter depends on the intended use. Different designs are used for different firearm actions and different user needs. Military users, for example, generally want BFAs to be very visible, so it is obvious to the user and observers that the BFA is attached, as discharging live ammunition through a BFA could cause a catastrophic failure. 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.

[edit] Gas operated and blowback firearms

A Marine fires blanks with the M15A2 Blank Firing Attachment attached at the end of the barrel, in an exercise in 2001.

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 propellent 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 adaptor 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.

[edit] Recoil operated firearms

Drawings from US patent 4,128,040, for a blank firing adapter for the short recoil operated M2 Browning machine gun.

Since blank cartridges generate very little recoil, far less than that produced by a live round, the recoil operation mechanism is not suitable for use with blanks. BFAs used with recoil operated firearms typically replace the locked breech of a recoil operated firearm with a simple blowback system using a restricted barrel, similar to a gas operated BFA. Short recoil operated pistols, the most common type used by police and military, are typically converted with a simple barrel replacement; the replacement barrel will lack the locking lugs to lock slide to frame, and will be built with an adjustable restrictor to control the chamber pressure. On designs with tilting barrels (again, the majority of modern designs is this) there may also be a provision for tilting the barrel back, simulating the unlocking of the slide — this is visible in US Patent 5,585,589 listed below.

One notable exception to the design of BFAs for recoil operated firearms are machine guns based on short recoil designs, such as the German MG42 light machine gun and its descendants. These designs use a muzzle booster to add energy to the recoiling parts, and muzzle brakes for these designs simply replace the muzzle booster with one that provides far more boost with blank cartridges. The M2 heavy machine gun, while it does not use a muzzle booster normally, can use a similar muzzle booster derived BFA.