Wednesday's Random Slang-o-rama: Fanning the hammer

If you are a fan of novels or movies set in the American West of old, you may be familiar with this phrase:

Fanning the hammer.

I chose it not so much for its obscurity but for the wonderful definition. Curious? Eager to know what it said?
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Okay! I'll not leave you hanging in suspense. So, here it is, for your reading pleasure, from Passing English (I promise to move on to a different dictionary soon!):

Fanning the hammer (W. Amer., 1886). Brilliantly unscrupulous. Instantaneously active, equal to energetic in the highest. Example of application of one term to varying meanings. Derived from West American gamblers wiring back the trigger of their revolvers, so that its stop-action is arrested. The six barrels of the revolver are discharged by rapidly striking back the hammer with the outer edge of the right hand, while the revolver is held in the left. This vibratory action of the right hand is the fanning. No aim can be taken, and fanning is only successful in a crowd. Six bullets will generally clear a crowd. So rapid is word adaptation in the States that already the term 'fanner' is used to describe an unscrupulously brave man.

I'll bet you a million to a bit of dirt that someone in this movie ended up fanning the trigger. Poster for the American western film The Gun Fighter (1917).