reason? I guess i think of it like this. In a survival situation i can have a 12 gauge shell in my gun loaded with a duplex #6/#4buck and be armed for small game and if needed defend myself a bit better then with just #6. I can even load #4 buck/00 buck and be well armed for big game or bad people and still have a better chance of hitting a bird or rabbit at 30 yards or further. For normal hunting i dont see an advantage to it. I carry what is best for the game im hunting. All that said i never was much for what other so called experts preach. I test MYSELF and find that theres alot of miss truths and down right bs wrote in books. Then add to that that alot of whats wrote was wrote back in the 50s and 60s (LYMAN) and is outdated and was done with different tests and technology of the day. Like i said if you doubt it just look at there outdated views on bullets bumping up to be accurate. Anyone that has shot A LOT of cast bullets and has done accuracy testing will tell you that 9 times out of 10 a harder alloy will shoot better then a softer one. Why would you expect any different. A bullet bumping up is a bullet deforming and isnt going to do it the same time every time. So basicaly your trying to make a varying blob of lead shoot small groups. Only thing i use the lyman manual for is they have loading data for some obsolete rounds that arent in other books. It was my first loading manual so yes i read it cover to cover. If a new loader asked me if he should id laugh and tell him to go and buy a modern loading manual like a speer or hornady. If you want knowledge on loading lead in ANYTHING come here. Theres a 100 times more knowledge on this forum then whats in the lyman loading manual. To me its about like thinking you can fix your new silverado by looking at a 1964 chev service manual.