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12 pr Armstrong (SS).This drawing was copied from a photograph taken on the day the Ultimatum was delivered. No vent piece can be seen so, if the drawing is correct, the gun is a muzzle loader. Note the small carriage. In the background are men of HMS Active's Naval Brigade.
"In 1859, Mr William Armstrong introduced his rifled breech loaders. The 6 pr 3 cwt RBL was originally intended for mountain service, but it was found to be too heavy. 7 prs were accordingly introduced for this purpose, and the 6 pr was restricted to normal colonial service, as opposed to mountain.
In the Armstrong system, guns were loaded through a hollow breech screw. The breech was closed by means of a vent piece, which was dropped into a slot or opening in the top of the breech. The vent piece was then pressed home against the chamber by means of a breech screw.
The shell was lead coated. On being fired, this soft coating was compressed into the 38 rifling grooves of the bore, and these gave it the required spin.
The Durban Volunteer Artillery (later Natal Field Artillery) took two of these guns to Cetewayo's coronation in 1873.6 pr RBLs were used in the campaigns of 1877 and 1878. Although two were with Col Rowlands' column at the beginning of the Zulu War, they do not appear to have been used in the war."
Source: The South AfricanMilitary History Society