SBML
Smooth Bore Muzzle Loading. The barrel is not rifled and the projectile is loaded via the muzzle of the barrel. All early cannons were of this type. British SBML guns of the mid-19th century were typically made of cast iron. The last cannon of this type in British service was the 68 pounder 95 cwt introduced in the 1840s. Modern weapons using this method of loading are light field mortars, in which the mortar bomb is dropped into the mortar barrel for firing; in these modern weapons the projectiles are spin-stabilised, but by fins rather than rifling.
Read more about this topic: List Of British Ordnance Terms