Shotgun Shell

12 gauge shotgun shells are the only types of 12 gauge ammunition in Fallout, Fallout 2, Fallout 3, Fallout: New Vegas, and Fallout: Brotherhood of Steel, and it is one of the types of 12 gauge ammunition in Fallout Tactics. It is marked "12-gauge shells, not for use by children under the age of 3."

Fallout and Fallout 2
A fairly common ammo type, the AC modifier of the shotgun shell will make it a titch more accurate than any of the other starting guns, until you get to .223 FMJ weapons. Even late-game enemies will use pancor jackhammers, making the shotgun shell a pretty valuable ammo type for any player.

Weapons using this ammunition

 * Shotgun
 * Sawed-off shotgun
 * City-Killer combat shotgun
 * H&amp;K CAWS
 * Pancor jackhammer

Fallout 3
The shotgun shell is common in Fallout 3 as it is used by almost all enemies that carry any shotgun weapon.

Locations
Shotgun shells seem to be found in almost every container possible. They can be found mostly in filing cabinets, Enclave crates, and are rarely found in desks. Almost every merchant has a good supply of shells, even scavengers and junk traders sometimes may have them in their inventory. The average amount you will find inside random containers is around 10, while the Scrounger perk will grant you up to 46 shells in case of high-leveled ammo crates. Also, gore bags are a useful but somewhat rare ammo source, giving you good amounts of ammo (average 24, up to 60 with the Scrounger perk). If you get around Evergreen Mills, Smiling Jack in the Bazaar will have around 70 of them in his inventory, if you want to steal some ammo with no karma loss.

Weapons using this ammunition

 * Combat shotgun
 * Sawed-off shotgun
 * The Terrible Shotgun
 * The Kneecapper
 * Double-barrel shotgun
 * Charon's shotgun

Fallout Tactics
Because one of your squad members starts with an Ithaca model 37 shotgun, 12 gauge shells are going to be one of the ammo types you need to snap up. They're actually more common in the very first mission compared to all the rest, but you should be able to keep an ample supply of them all the way to Vault 0. They aren't the best rounds for the shotgun, but because flechette, slug, and EMP shells are very rare, they're going to be the ones you use the most.

Fallout: Brotherhood of Steel
Shotgun Shells are slightly common in Fallout: Brotherhood of Steel but not exceedingly so. They can be found in containers and possibly as loot dropped by enemies (usually by those using shotguns).

Weapons using this ammunition

 * Double-barrel shotgun
 * Combat shotgun

Amunicja kal. 12