[Neil Young]

You can hopefully narrow down the problem by removing the cannon (the receiver, barrel and toggle assembly) from the frame. Do not remove the toggle. Pull the toggle up and all the way back and push it back into battery. This should insure that the firing pin is locked back and ready to be released. Press on the forward end of the sear bar near the spring loaded plunger on the front. The sear bar should rock around a central pivot pin and release the firing pin (striker). If it clicks, then the striker has released forward. If not, then the problem is in the sear/toggle area. If it does click and is repeatable, then the problem is probably in the trigger/side plate area, assuming that the sear plunger is free and smooth as mentioned by others above. If what I am saying is not clear, then others may expand or correct. Try it.