Combat Shotgun (Fallout: Brotherhood of Steel)

''This two-handed shotgun rapidly fires a thick, deadly blast of pellets. This weapon can't be bought, though; it must be earned from fulfilling a side quest.''

It's a powerful weapon for chapter 2 and not bad for chapter 3. And if you have a high Critical Chance, it gets even better.

Locations

 * Bridge West, available from Hieronymous
 * Bridge East, in a footlocker on hidden island
 * Docks Holding Pens, can be bought from Salieri
 * Vault-Tec Warehouse Basement, in a footlocker
 * Vault-Tec Warehouse Basement, purchased from Shop-Tec terminal
 * Vault Residence Level 1, purchased from Shop-Tec terminal
 * Vault Laboratory Level 2, in a shelf

Trivia

 * The SPAS-12 was designed in the late 1970s by the Italian company Luigi Franchi Spa as a special purpose, military and police close combat weapon (actually, SPAS stands for Sporting Purpose Automatic Shotgun, or Special Purpose Automatic Shotgun, depending on the source). It featured a selective action for greater versatility, and can be used as a gas operated semi-automatic repeater or as a manually operated pump action repeater, depending on the mission and ammunition used.