I have the same problem with the same screw on my repro 16/20 set. I tightened it a couple of times & finally used some low strength Loctite to solve the issue.

Be sure if you use a thread locker to clean the screw & hole so it is grease/oil free. Then use very little Loctite, just a small drop off the head of a tooth pick is all that's needed on a screw like this. The biggest mistake people make with Loctite is they use too much of it & create a bigger problem than they are trying to solve.

That's the truth. A while back, I bought a gun and wanted to remove the stock to send up to Chris Dawe. The top tang screw would only turn so far till it stopped. Turned out, a previous owner had used loctite to keep the screw timed, instead of fitting a new screw, or shimming beneath the tang to keep it tight. They obviously used way too much loctite, and when they put the screw back in, managed to cement the screw to the threaded sleeve in the stock. Turning the screw was also turning the sleeve until it came up hard on the underside of the tang. All is well now, but it took a wrench on the screwdriver shank and some serious effort to break the cement bond. New screw, properly timed, now fitted.

That same screw on my 20 repro disappeared while shooting doves. I had never noticed it being loose.
Guess I need to replace it.

Ok, so my problem is more than an isolated occurrence. What exactly does that screw retain? What function does it serve? Yes, I looked at the schematic available via the homepage technical tab and that is about as clear as mud. Is there an exploded view somewhere that I cannot seem to find?

Gary, The floorplate (trigger plate) is held to the receiver with those three screws, forward of the triggers, and tang screws behind the triggers. With that one screw loose or missing, I doubt the trigger plate will move downward. When you cock the gun, The cocking slide moves forward and the pressure of the hammer springs could want to move pushing against the trigger plate, but the whole assembly is quite rigid, with two tang screws and the two forward trigger plate screws.