I grew up with a nice L.C. Smith .410 set up for skeet and found early on it averaged a little over 70% in a 20 inch circle at 25 yards – full choke in both barrels. The short shells averaged fractionally tighter, but the more shot in the shell the more holes in the center part of the pattern. For some time I have reloaded 2 1/2 inch and three inch shells. The difference on 45 yard teal is remarkable. Of course, one reason is the 2 1/2 inchers are loaded with 8 1/2 shot and the 3 inchers get either 8’s or 7 1/2’s – all magnum shot.
My father and I have taken much game with the 3 inch shell and 7 1/2’s over the last 50+ years with this gun and it has always performed very well. On Stuttgart ducks the crippling rate was no more than with the M12 trap gun. It works well on mallards to 35 yards. Doves and quail are duck soup – excuse me – dove and quail soup. If you want to really tighten up the pattern, try Lubaloy 7 1/2’s or their equal.
You use a 410 on mallards? I confess that I have never tried that one, but I do agree with you about how the 3″ .410 works. Yes, they don’t pattern quite as tight as the 2-1/2″ shells do, but the extra 3/16 oz (77 #8 pellets) do have to go somewhere and it isn’t too far from the center. Still, even a 3″ 410 requires an expert shotgunner compared to a 28 gauge or larger.
Bob Brister’s book “Shotgunning, the Art and Science” has some nice work on 410 patterns. He does introduce the problem of excessive shotstring in the 3″ 410, something that I do not have the facilities to measure. Still, as bad as the 3″ 410 is, it is almost certainly better than the 2-1/2″ shell as far as pellet count where it matters goes. This isn’t a percentage thing.
The 410 is a demanding little game gun and it is a compliment to your skill that you feel confident using one.