Posted by Dakota raised on May 04, 2003
Flintlock rifles can be fired from full cock or half cock but only work well from full cock.
I find this site interesting, but had to disagree somewhat with this meaning and origin.
Flintlocks, as well as any 'hammer gun', that is to say a gun with an exposed hammer such as all the lever action Winchesters and Marlins and single action revolvers have a sear (notch) in the hammer which holds the hammer at 'half cock'. This is the 'safty'. If this sear is worn or defective the gun can go off unexpectedly, or "go off half cocked".
I have always understood the meaning to act in a manner not expected, usually anger.