The lightest 12 ga load I've seen was a handload using 3/4 oz of shot. I found it in one of Micheal McIntosh's books. It is also a PITA to load, it requires a number of filler wads which are time consuming to put in. I have reloaded 1/2 oz 20 ga loads but they are just as much trouble and the load I use is safe but not published. I have also seen loads using IMR SR 7625 in a shooting digest but can't remember which one. I'm not sure of the reasoning behind dropping pellet count, is it to approximate the pattern density if you use larger shot when hunting? If so, then the target's surface area would have to increase to match the area of the game bird you are hunting. I just use the same target loads as always and shoot more often. The center of the pattern is the same and a centered target, whether clay or feather, is a dead one. By the way, 2 1/2" factory 410 loads are in the 1200-1250 fps range. The new Winchester HS loads are a little faster still. The factory 3" shells move much slower, a little over 1100 fps.