The Siler frizzen spring looks like a ski ramp. The frizzen really has to go uphill to snap open. The top "arm" of the spring should be as horizontal and flat as possible, and it snaps over smooth and fine every time.
The "snapover point" is right at the little clearance notch on the spring. Which is right where the flint reaches the very bottom edge of the frizzen. Perfect harmony.
With the cock down, the frizzen will not stay down if you push it down. Push it down to the flint, and turn it loose, and it snaps open with authority.
If you look at a lot of 18th century locks, you will notice that their frizzen springs tend to be very straight, and very horizontal, avoiding the problems you get with a very curved spring....something that plagues several modern made locks.