The slot in wheel system is the earliest known type of self opening pan . It isn't always appreciated that , apart from keeping the powder in the pan, the automatically opening pan is important to how wheelocks work . Although they will spark up with the pyrites resting directly on the wheel this isn't very efficient as the spring has to accelerate the wheel from rest as well as overcoming the friction of the pyrites. An automatically opening pan allows the spring to first accelerate the wheel , then drops the pyrites smartly onto the wheel when it's turning at its maximum speed. Hence a much better spark.
The single spring locking bar is certainly simple but perhaps not as foolproof as it appears. The danger being that it is only the tension of the spring that holds the sear into the wheel rebate. With the possibility of it not fully engaging and the thing going of by accident. Hence the development of the double locking arrangement where the sear is positively locked into the wheel using a secondary sear lever.
The other lock illustrated has an early form of hook type pancover where the cover and the operating arm are one and the same . The cover is opened by a cam or pin on the wheel . Early Portuguese locks use this very simple system
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