Shotgun Ammo

Shotgun ammunition is described by three numbers that all matter: gauge, shell length and payload. Gauge must match the barrel exactly. Shell length must be equal to or shorter than the chamber — a 3-inch chamber takes 2¾-inch shells happily, but a 2¾-inch chamber must never see a 3-inch shell.

After that it is about what the pellets are doing. Birdshot carries many small pellets for clays and game birds. Buckshot carries a few large ones and is the standard defensive load. Slugs are a single projectile and turn a shotgun into a short-range rifle, though a smoothbore barrel and a rifled slug behave very differently from a rifled barrel and a sabot.