A steel tube through which a projectile (bullet, slug or shot) will travel through from the firing chamber till it exits at the muzzle end. The chamber end often has either a forcing cone (Revolvers) or normally a larger shaped hole (firing chamber) that will accept a complete cartridge/shell for detonation (firing). The length of tube from the firing chamber to the muzzle may be smooth bore or rifled or Polygonal rifling. (See Rifing).