If you look at the ballistic charts for shotshells, they typically give you the weight of the shot charge, (1 oz, 1 1/4 oz, etc) the shot size, (no. 5, no. 8, etc) and either a velocity number like 1200 fps or a number indicating the power level (which went back to drams of black powder) then there are several choices of what the actual shot pellets are made of. the cheapest shells have soft lead pellets, the premium shells use hardened lead. The non-toxic bismuth or heavishot are the most expensive. You can't leagally use lead for waterfowl, and some other places now restrict its use completely. Some shotguns pattern one charge weight a lot better than another, or one power level better than another, so it can get pretty complicated finding the best combination for any particular use, then you can change chokes and start all over again.