
Here's a photo of the main SST parts and their approximate relationships to each other. Yes I know the trigger is missing its adjustment screw and the hammer is missing its safety notch but these were the only orphan parts I could find in a hurry for the photo.
Please notice the small secondary set sear ledge on the front of the kicker; this is captured by the hook on the top of the secondary set sear as the trigger is pushed forward in the act of setting it. This setting action moves the kicker downward and away from the primary sear, allowing more sear travel into the hammer's safety notch but also moving the kicker (now set) farther away from the primary sear and so making it more difficult for the kicker to trip it when finally released.
The key to the entire arrangement is the SST kicker spring, shown at the right side of the photo. It's much stronger than the standard kicker spring and its forward end bears on the two kicker pins shown at the upper right end of the kicker. These two pins each have their own bearing point across the active end of the spring, and the relative positions and dimensions of these bearing points will determine the angle of the kicker and how it bears against the sear when at rest. By adjusting these bearing points relative to one another, the 'at rest' position of the kicker can be set so that it is A)far enough from the sear to allow the sear freedom to fall into the safety notch at all times and B) close enough to the sear so that the inertia of the kicker & spring will fire the rifle reliably and without too much lag time.
This is a very narrow window of adjustment, and is normally achieved by careful stoning or grinding of the two bearing points of the kicker spring. The relative positions of the different parts are dependent upon their dimensions, and variations are common among parts from different sources. And please believe me that many of these old rifles have received parts from MANY different sources over the years. Hand-fitting is the rule and a good understanding of the parts' actions and relationships is important for achieving good results.
I realize this is only one quick photo and a hurried exposition of the basics, so please ask more specific questions if/when necessary. I enjoy a little 'pay-forward' of acquired experience and it helps me to organize thoughts for a future article.
Regards, Joe