Sorry, my original response was erased Tuesday night when I lost connection on my end. Work, sleep, and shooting took up the rest of the time until now. I'll have to write quick, hopefully I can sneak this in before I get rebooted.
Yeah, that is a little confusing. Suffice to say, I think duplex loads are an answer to a problem no one ever had. They are a compromise combining the worst attributes of each shot size. Adding larger shot to smaller shot does nothing other than to potentially lower the number of hits on the target. What few larger shot that are in the load are not adding much to "knock down" as they unlikely to have a couple make contact with the target. If penetration is needed, go with all larger shot to get the shot totals up for best patterns with that size.
I am not much into "long range" shooting of game animals, the longer the range the more likely the odds of something going amiss. Rangefinders and Internet applications can help a rifle shooter but most birds fly fast enough that ranging the target, entering the data into an app, and then using that information to make the shot would put the bird far enough away to need a rifle.
Dropping a bird "way out there" is also harder to locate, even with a good dog. If merely wing tipped, the more distance between the rooster and dog/shooter the more likely the bird is to be lost. I've shot more than a few roosters at typical range that still gave the dogs the slip. I would not feel good with the odds at greater range.
I've used most, if not all, the various lead substitutes to one degree or another. I've used Hevi-shot the most followed by Federal's discontinued tungsten/iron and tungsten/poly offerings. I shot a couple cases of Hevi-shot at waterfowl and pheasants and however many 12 ga rounds fit in a 50 cal ammo can and a 30 cal ammo can of 20 ga of the Federal loads. I also loaded and shot a 25 pound bag of the tungsten/poly before it was pulled. I've reloaded Hevi-shot too, a couple jars of #6 shot for pheasants and a couple more of 12 shot for crows. The latter from a 20 ga knocks crows down like a 2 1/8 oz load of 7 1/2 from the 10 ga.lll I've used Hevi-shot Classic Doubles, Hevi X, and Fiocchi Tundra the least, maybe 50 each of the end ones and 100 of the middle.
I didn't think poorly of any of them though the Federals seemed a bit light on shot count and the Classic Doubles were slower than molasses and messed up my leads at first. Loads moving faster than 1200 fps quickly began to add up on recoil but little in down range effectiveness. #4 or 5 lead shot will run out of pattern density long before individual pellet lethality.
I think these steel alternatives shine in the smaller bores but are generally unnecessary in the 12 ga. I see a lot more wild birds under 40 yards than over and gear my equipment for those likelihoods. .
