Way back when as I understand it, there were generally two classes of shot known as Drop & Chilled. R'Man can likely correct any inaccuracies here. Essentially they were both made by an identical process. The shot was poured through a vibrating sieve from atop a tower & caught in a large vat of water. So in effect both were "Dropped" & both "Chilled". The difference was as R'Man stated the amount of hardening alloy content of the lead. As I understand it the fall of the shot through the air allowed it to cool sufficently & the water in the vat quickly became heated to the point the "Heat Treating" affect didn't take place.
The Magnum shot would come along at a later date with a still higher alloy content than the Chilled.
