Hi Dave,
When I balance the springs, I start with the force needed to open the frizzen being about 30% of the force required to pull the cock back from rest to full cock. I measure those forces with a small digital luggage scale. However, that is just my starting point and the geometry of the lock can alter those forces. For example, if the lock has a large large tall frizzen on which a flint gets a long scrape, I may want the force to open it lower than my starting point. In contrast, if the frizzen is small and throw of the cock short, like on late English flintlocks, I tend to want stronger force to open the frizzen. Jerry is right that the frizzen spring just has to be strong enough to hold the pan cover closed, however, I've experimented a lot with these forces. I find that idea works fine until the frizzen gets covered with fouling. That is when you want more resistance from the frizzen spring to allow the flint to scrape through the greasy fouling and make sparks. When I tune a lock, I am not thinking of how fast it is on the first shot, rather how fast and reliable it is on the 20th or 30th shot when the lock is dirty and flint worn. I used to start with a ratio of 25% but after experimenting and more experience with different locks firing under a variety of conditions, I upped that initial ratio to 30% and may go a little higher in the future. The photos below show a Chambers round-faced English lock that I tuned. The frizzen force is about 25% of the mainspring force because the frizzen is tall and the flint makes a long scrape. The first photo is using a clean, sharp flint. In the second, the flint was reversed so the dull side faced the frizzen. In the third photo, the dull flint and frizzen are covered with inletting black and soot. Finally, for the last 2 photos, I used a rounded piece of quartz from my driveway as a flint. The frizzen and rock were clean when fired. That is the kind of performance I want from a flintlock.
dave
