The wheel-lock mechanism used a fluted or grooved steel wheel located above the priming pan and held under tension by a strong spring. The bock was also regulated by a spring and fitted with a piece of iron pyrite.To fire the gun, the lock was wound up with a key, then the cock was let down on the priming pan, so that the pyrite rested on the wheel. To ignite the powder in the pan, the trigger was pressed which caused the wheel to be released and spin round quickly. The sparks produced then ignited the powder. The lock was not only complicated and expensive but also prone to damage, which prevented its wider adoption. Wheel-lock and matchlock combinations were fairly common because many wheel-lock mechanisms were unreliable. Such a gun would function as a regular wheel lock, but if the wheel lock broke or malfunctioned the user would still be able to fire the gun using the matchlock.