The biggest difference is the shot. Premium shells use magnum shot which is a harder alloy rather than pure lead. Pure lead is too soft and flattens out, often not penetrating into the vitals. Magnum shot often exits after passing through. In order of hardness with softest first are: pure lead, then chilled lead, then magnum, and then plated. Above that are the various heavier than lead shots.
Usually the other components are better also, but shot is the biggie.
I disagree that plated is harder that magnum or high antimony shot not so most plated is chilled with plating. Some of the high end nickle plated is indeed harder and some isn't. MB
