While we're at it
"Slugs" have become sort of diversified too. A traditional "Foster" slug is a thimble shaped piece of lead, solid nosed and hollow based, just under bore diameter. (.69 cal?) In 12 ga/2-3/4 shells they typically weigh 1 oz, although some of the old 7/8 oz slugs are likely out there, and the 3 and 3.5 mag slugs can be a bit heavier. Velocity in the neighborhood of 1250 fps. Slugs turn a shotgun in a single projectile weapon, and add a bit of range and penetration and are useful on soft skinned deer/hog/black bear sized game. They are serious bad news on human targets too.
Then there's "Brenneke" slugs, which are a sort of improved Foster. The Brenneke's use a wad arrangement in the base, and I believe they are hardened lead as opposed to the dead soft lead of Fosters. Not sure on that.
The more recent slugs are "sabotted", meaning the projectile is encased in a synthetic cup which discards after leaving the muzzle. The projectiles can be varied in their shape, and some even use a handgun or muzzleloader slug in the cup. Since these slugs are very sub caliber in relation to the bore, they are lighter and faster. The sabot is often used in conjuction with rifled shotgun barrels to give near rifle like accuracy.
Shotguns need a sight system beyond the classic single bead, to really get full benefits of slugs.
