RML 40 pounder gun

The RML 40-pounder gun was a British rifled muzzle-loading siege and fortification gun designed in 1871. It was intended to supersede the RBL 40 pounder Armstrong gun after the British military reverted to rifled muzzle-loading artillery until a more satisfactory breech-loading system than that of the Armstrong guns was developed.

Description
The original Mk I short barrel of 18 calibres suffered from irregular velocity and hence accuracy, due to incomplete burning of the powder charge, hence only 20 were built.

Mk II of 1874 with barrel lengthened to 22 calibres solved this problem and became the definitive model.

The gun consisted of a central toughened steel "A" tube surrounded by wrought-iron coils, with a trunnion ring and cascabel. Rifling was the "Woolwich" pattern of three broad grooves, with a uniform twist of 1 turn in 35 calibres (i.e. in 166.25 inches).