These are basically an improvement and simplification of the snaphaunce lock. The frizzen now has the pan cover made onto the bottom of it and the sear is simpler. Many snaphaunces were modified to this type of lock as they were sent in for repairs. In general these became a common lock by about 1650, there have been quite a few turn up in archeological sites and in collections all over America. The fantail stocks on these early guns actually hold better than most modern stocks.