A blank firing attachment, or "BFA", is a small device which attaches to the end of a
gun barrel to allow the use of
blank cartridges. It is
required when using an
automatic weapon (at least on "full auto" setting) with a gas-operated mechanism. This type of
firearm uses some of the expanding
gas from the exploding
cartridge to blow the
bolt back and
chamber the next round. Blank cartridges have no bullet, and so there is nothing "plugging" the barrel (albeit briefly) to maintain this gas pressure. This is the function of the BFA. It allows automatic weapons training without giving real
bullets to
nervous recruits (a definite
bonus).
At least on the M-16 I used in the Reserve, the BFA does not completely plug the barrel end, thus retaining a satisfyingly Robocop-esque star-shaped muzzle flash...