First, act alone. I don't know when you were born. Did you play with toy matchsticks made of bicycle chains when you were a child? The firing pin of that toy gun has to lock the trigger back by hand every time, and then pull the trigger to fire. If you want to fire again, you must pull the firing pin back. This is a single action, embodied in the left wheel, that is, before each fire, you must grab the hammer on it and pull it back with your hand, which is often seen in early cowboy movies in the western United States.
Second, double action, or take toy guns as an example. There used to be a plastic revolver filled with small red circle propellant. Pulling the trigger will ring, and the small hammer at the back can automatically open and hit the primer without pulling. When you pull the trigger, you don't need to pull the hammer back manually. This is a double action, and the principle is the same as a real revolver.
So, what's the difference between single action and double action on a revolver? In fact, it is the difference in trigger firing components.
The trigger of a single-acting left wheel can only act as a one-way lever, that is, release the hammer. Double-acting revolver is a two-way lever. When the trigger is pulled to a certain stroke, the hammer can be pushed up, and if the trigger continues to exert force, the hammer will be hammered down. This is the difference.
In addition, both single-acting and double-acting revolvers can push the hammer backward or even forward by hand to speed up the firing speed. This method was patented by cowboys in the early western United States and is now used in many IPSC revolvers.
Now we can know that the single-action revolver or the double-action revolver is actually only the difference between the trigger part and the locking mechanism. They are the same. They aim the bullet chamber at the barrel by turning the wheel seat, which is why people have always said that the air tightness of the revolver is not strict, because its locking mechanism is actually the piece of metal near the hammer head of the pistol. And the wheel seat can be regarded as a gun bore, understand?