maybe it's part of the whole Western convention of "fair fights," ie. you can't fight someone with a pistol if you have a rifle and he is out of your range; so he uses the rifle to shoot the horse and force Calloway into the "duel," then it's a fair fight, pistol vs. pistol. That could also be why he waits till Calloway is within Calloway's pistol range before killing Calloway, all part of the "fair fight" convention, eh?
