The Armstrong rifled breech loading guns represent the first significant change in artillery design in over 400 years. Loading from the rear was accomplished by removing a special vent piece, placing in a spherical shaped projectile and propellant bag and then replacing the vent piece and closing it into position using a special weight lever. The barrel was rifled which imparted spin on the projectile when it was fired. This provided improved accuracy and increased range.

7 inch R.B.L. of 72 cwt. and 82 cwt. The 82 cwt. gun was first issued in 1861 as a 100 pounder sea service gun. After February 1862 the weight of the shell was increased to 110 pounds and the gun was so designated the 110 pdr. After 1864 it was finally known as the 7 inch RBL. 883 of these guns were manufactured.

Six different natures of Armstrong gun were introduced into the service, the 110 (7-inch), 40, 20, 12, 9 and 6-pounders Although Armstrong himself stated he did not believe his system suitable for guns heavier than field, so anxious were the Navy to re-equip they ordered 100 110-pr (7-inch) RBL guns without any trials of a prototype! Then when they found the heavy vent pieces extremely difficult to handle in a rough sea they demanded the return of the old guns. Two of the 110 pounder guns were obtained for use in NSW. Records indicate they were held in Naval stores since 17 November 1866 and 15 may 1867. The 1870 commission recommended they be placed at Inner South Head near the lower light house. Mention has also been reported they were to be placed on Fort Denison but it is doubtful that the guns were ever actually installed.