What does "gauge" mean anyway? As used here gauge means the number of round lead balls the same diameter as the inside of the barrel (aka the bore) that it would take to weigh one pound. It takes 12 lead balls the same diameter as a 12 gauge barrel to weigh a pound. The smaller 20 gauge would require 20 balls of that barrel diameter. The larger bore 12 gauge would require 12 lead balls of the bore diameter to weigh one pound.
In general the number of pellets in a shotgun shell is greater for the bigger bore guns. A 12 gauge is a larger diameter shell than a 20 gauge. So when using the same sized shot the 12 gauge will throw more pellets than the 20 gauge per shell.
Similar to the numbers used to designate gauge, shot size is also inverse to the number designation. The smaller the number - the larger the pellet. #9 shot is very small pellets suitable for bird hunting. #8 and #7 sized shot is common for use in trap and skeet shooting and also suitable for hunting the smaller game birds like partridge and pheasant. #6 shot is a decent rabbit load. #4 and #5 is a larger pellet suitable for turkeys. #2 shot is suitable for goose hunting. #1 shot is big O, OO, and OOO are bigger pellets sometimes called buckshot. In general the larger the pellet, the more deadly it is when it hits large game. The trade off is that you fit fewer pellets in each shotgun shell.
A shotgun "slug" is one big pellet as big as the bore in your barrel (like a rifle bullet). For self defense any shogun shell will kill at close range, but #1, O, OO, and OOO are considered man stoppers.
As a rule of thumb, the longer the shell the harder it will kick. You can use shorter shells in longer chambers but not the reverse, so buy the 2 3/4 inch shells and use them in any shotgun of the correct gauge. The shorter shells will do everything you want at under 50 yards. If you decide that you want to extend your range or need more power you can work up to 3 ½ inch shells but don’t start with them.
This should give you a good basic knowledge of shotgun shells and the terminology associated with them. In the next installment we’ll look at which shotgun to choose.