Tap Rack Bang

Tap, rack, bang (TRB) is jargon for the emergency corrective procedure for a semi-automatic firearm or an automatic firearm after a failure to fire ("stoppage"), which usually gives an audible "click" as the firing mechanism fails to fire a round. This sound tends to be trained to act as a reactionary cue to commence the corrective prodecure, unless the operator knows the magazine is simply empty. The procedure is effective for most common failures, such as defective ammunition or improperly seated magazines. In British military parlance these drills are called "Immediate Actions".

#Tap refers to the first action; that is to tap the magazine. This is to ensure that the magazine is properly engaged in the firearm.
#Rack refers to operating (cocking or cycling) of the slide of the firearm. This will serve to eject a miss-fired round – that could be a possible cause of the stoppage – and chamber the next round.
#Bang simply denotes the action of firing the firearm following the first two steps.

While the 'Tap, Rack, Bang' is effective in the vast majority of cases, it is not effective in all cases. Some failures, such as a case becoming lodged in the breech or breakage of the firearm, require more complicated maintenance or even attention from a gunsmith. However, under emergency conditions (such as combat) it is still the first procedure followed. It rules out most simple cartridge-related failures of the weapon and should be done before field-stripping the firearm to gather further information. It is also advisable to execute this drill before taking additional time to produce and use a back-up firearm.