shot

multiple pellets in ammunition#^faa15f

are multiple sizes: typically larger shot is for larger targets.

smaller number is larger diameter

"magnum" means it has more gunpowder. if the gauge/length are the same, it's interchangeable.

steel shot

not as dense as lead. will have less spread. use one to two sizes larger than lead.

Required for waterfowl hunting, to prevent lead poisoning in waterfowl