2-3/4 dram 8's work just dandy for 16 yard ATA Trap and Trap Doubles, but start to loose a bit beyond the 20.
Yes, I know, 8's can break targets from further back, but 7-1/2's have proven themselves over the years.
The best 3 dram 7-1/2's you can get your hands on are for the back fence. My all-out favourites are
Federal Gold Medal Handicap papers (T171's) ... a bit pricey and often hard to get ... but they work !
Second choice is Remington Premier Nitro 27 Handicaps. Both also make very good Sporting Clays loads for
distant presentations, rabbits and battues !