The next refinement was to improve the arm or 'serpentine' as it was called, by spring loading it and arranging a trigger and trigger release so that it moved forward into the pan and backward away from the pan by mechanical means. The touch hole was improved by forming a pan to contain the priming powder and this pan was provided with a hinged cover to prevent the priming from getting wet or blowing away prior to ignition. It was at this period that a certain amount of experiment was made with both rifling and breech loading methods, but did not meet with much success. It is generally believed that the wheel-lock was invented about 1517 in Nuremburg. Leonardo da Vinci wrote a description of it and claims to have fired it.
All early specimens are of German manufacture.
The mechanism was similar in principle to the modern mechanical petrol cigarette lighter. A serrated steel wheel was mounted near the flash pan, and a piece of iron pyrites fixed in a clamp was pressed against the periphery of the wheel. A spring was attached to the shaft of the wheel and a key was supplied to wind up the contraption prior to firing. The trigger secured the wheel in the wound up position. Pressure on the trigger released the wheel which revolved under the pressure of the spring and showered sparks into the priming pan.