Shotgun (particularly known as scattergun or historically as a fowling piece) is a smooth-bore type of firearm that is basically used for firing from the shoulder, which works with the energy of a fixed shell to fire a number of small spherical pellets called shot, or a solid projectile called a slug. Shotguns come in a wide variety of sizes, ranging from 5.5 mm/.22 inch bore up to 5 cm/2.0 in bore, and in a range of the following firearm operating mechanisms: breech loading, single-barreled, double or combination gun, pump-action, bolt-, and lever-action, semi-automatic, and even fully automatic variants. In Space Monsters universe, shotguns are often used by Terran people to go against the alien invasion.