Hi Allan,
A strong spring is faster but more important, it depends on the lock. A Siler, like many similar locks, has a fairly long throw to the flintcock. That long arc allows a light mainspring to power the flintcock and flint and produce good sparks. That makes for longer lock time but is, as you say, easy on the flints. In my experience, on late period flintlocks with a short throw, that situation does not work very well. The flintcock simply does not have sufficient arc to build up momentum. The short throw and powerful mainspring mean quick lock time and sure sparking for those locks.
Let me share some insights on lock springs I gained while building my Wogdon dueling pistol locks and handling some fine late flint period English dueling pistols. I would love to hear from Bob Roller on this. All of the locks on those pistols, including mine, had roller bearings either on the frizzens or on the feather springs. All of the mainsprings were powerful but all of the feather springs were relatively weak. However, the roller bearing boosted the pressure of the frizzens on the pans of the locks. It took considerable force to start the frizzen forward when struck but once over the apex of the roller or hump on the feather spring, the frizzen kicked over with almost no pressure. It would bounce back slightly until the toe of the frizzen was stopped by the hump or roller on the feather spring. The frizzen exerted strong resistance to the flint for only that instant of strike and then it was as if the feather spring was removed. Ever since that experience, I've made fairly strong feather springs on my locks without roller frizzens to provide firm pressure to keep the pan closed, provide some resistence to the flint strike, and prevent kick back. On locks with roller frizzens, I mount weak frizzen springs and let the roller do the work. In all, I install strong mainsprings because I like fast locks and I demonstrably shoot better with them.
dave
