Well, it's been a while since I had an Uberti with that type of hammer.
I seem to remember messing about with the screw. As I said, there is a very small spring and a plunger under the screw. The plunger extends down through the hammer and comes out near the 'safety notch' on the hammer. As I recall, the plunger is what makes the hammer block work. The little spring pushes the plunger down and shoves it out of the hammer to engage with the notch on the hammer. I seem to remember fooling around with the screw, and all tightening the screw did was increase the spring pressure. Back the screw out carefully, so the little spring doesn't go flying and you will see what I mean. I got rid of that revolver a long time ago, but I seem to remember everything worked fine as long as the screw was flush with the top of the hammer. Don't let it unscrew any further than that.
That's about all I remember about that style hammer block..
