That act of raising the pistol vertically while cocking it after firing a shot allowed the spent cap to fall off easily and also gave the appearance that the shooter was raising his pistol to "throw" lead at a target.

The Dance and Brothers pistols were made without a cylinder back guard cast into the frame. That feature allowed the spent cap to fall off easily when the pistol was raised vertically and cocked after firing a shot. The caps often jam between the frame and cylinder when cocked after firing a shot on pistols with a cylinder back guard.The back guard prevents the spent cap from falling off and then it jams the cylinder. Sometimes on pistols with a cylinder back guard, the pistol must be shaken or the spent caps must be picked off after firing. That can be disastrous in a gun battle when the shooter is firng multiple and rapid shots or "fanning" his pistol.

I have always heard that was where the act of "throwing lead" came from. That theory was recently confirmed by David Carridine's "Wild West Tech" on the History Channel.