The Wheel Lock's firing mechanism is a vast improvement from the risky one employed by the Matchlock. The revolving wheel was powered by a V-shaped spring that was attached to the wheel's spindle by a short chain. When the trigger was pulled, the wheel revolved and hooked a key or spanner over the outside shank of the wheel. The chain wrapped around the spindle and this compressed the spring. The pyrite was held by a small vise mounted on a pivoting arm known as the dog head. A spring on the lock below the arm that provided the downward pressure needed to ignite a spark in the pan.
The loading and firing was a simple process. First, the wheel was wound. The charge was then placed in the barrel and the pan filled with priming powder. A cover was slid shut over the pan. When the trigger was pulled, the pressure released the sear from its lodging and the wheel was then free to turn. When this happened, a cam attached to the wheel struck a bar on the pan cover and opened the pan and the thus the dog head was forced on the rotating wheel. This created a series of sparks and ignited the priming powder in the pan.