I found careful polish job is much better then messing with the nearly useless screws.After a polish? Then try the screws as burrs are out of the equasion.A burr can cause issues in a big way.
Pappy,Home Depot has them -> (2) for .99 Just take 1 out of the trigger and get the next size bigger. I have only replaced the most forward screw.Round end and polish w/600. It doesn't take much more length to make a much lighter trigger .Be careful............. could misfire easily......