Some years ago I read that, back when the cap and ball revolver was king, the Colt design was not considered entirely safe. The tiny pins in the cylinder, that mated with a notch in the hammer's nose, had a habit of breaking during rough use.
Thus, it was not uncommon to carry the Colt cap and ball with the hammer down on an empty chamber.
We pamper our cap and ball revolvers today but in its day it saw a lot of hard use. Falling from a horse was a common occurrence, and if you landed on the revolver it was rough on the gun (and your hip, ouch!).
If the pin broke, or the cylinder was somehow forced over and the hammer came to rest on a live percussion cap, this would be easily unnoticed. From then on, the wearer was walking around with an unnoticed accident waiting to happen.
So, the pin breaks. The cylinder indexes over. After chuck, the cowboy throws his saddle on the horse and, to get the stirrup out of the way he puts it over the saddle horn while he tightens the saddle. The stirrup slips off the horn and lands squarely on the exposed hammer of his Colt, which is resting on a live percussion cap. BANG! A bullet is through his thigh or knee!
This isn't fanciful. The late gun writer Elmer Keith said a number of old cowpokes were crippled by this accident, but usually because they'd loaded their SAA with six cartridges insead of five, and left the hammer in its weak "Safety" notch.
At the range, I load all six chambers. In the field, I load five and put the hammer down on the empty chamber. The cylinder cutouts for the nipple are deeper and stronger than the pin.
