Tap rack bang

Tap, rack, bang (TRB) or tap, rack, and go is jargon for the response to a failure to fire in a firearm with a removable magazine.[1] This is designed as an unhesitating "Immediate Action" and involves no investigation of the cause (due to being under fire in a combat or defensive situation), but is effective for common failures, such as defective or improperly seated ammunition magazines.

1. Tap - to tap the magazine. This is to ensure that the magazine is properly/completely inserted in the firearm so that it feeds properly. As typically taught in tactical firearms courses, the "tap" is considerably more than a tap, and in the case of a semiautomatic pistol is usually accomplished by slamming the gun hard into the palm of the other hand, magazine end down.
2. Rack - pull back sharply and then quickly release the action/slide of the firearm. This will eject a misfired round, which could be a possible cause of the stoppage, and to chamber the next round.
3. Bang/Go - aiming and firing the firearm again. If the firearm again doesn't fire or fails to extract the spent round, it may indicate a more serious problem with the firearm, requiring maintenance. For instance, if the firing pin is too lightly striking the primer on a cartridge, it may indicate a worn-out spring or firing pin.

Some failures, such as a "stovepipe," require more complicated maintenance or attention from a gunsmith. With others, such as a squib load, the "tap, rack procedure" should never be used.[2]

References

1. Tong, David, "Trigger Options of the Semi-Automatic Service Pistol"
2. "IMMEDIATE AND REMEDIAL ACTION - M9 SERVICE PISTOL", Marine Corp Development Command, p. 7, archived from the original on 2014-03-17, retrieved 2016-03-07