Although the Marshal has only one silver bullet, he uses it to shoot gang leader Lou Compton in the shoulder. In the fight that follows between the Lone Ranger, Tonto and the other two Comptons, the Marshal disarms Lou Compton and thus has another loaded gun.
Toward the end, Marshal Frank Dean has an empty pistol while the outlaws hold the Lone Ranger at gunpoint. The Lone Ranger mentions a silver bullet, then the marshal remembers he has a silver bullet in his pocket. He loads the gun with the bullet and wounds one of the outlaws, allowing the Lone Ranger to take control of the situation. Then the Lone Ranger tells the marshal to cover him while he rounds them up even though the gun is now empty again. When they all go outside, the marshal is still holding the outlaws at gunpoint with the empty gun.