The Gun - Rifled Ordnance: Mountain Artillery (now called Pack Artillery)
OrdnanceUp to 1864 the RBL 6-pr (2.5-inch) 3-cwt gun was intended to be used in the mountain role but was found to be too heavy so was issued to colonies as a light field gun. Some were shortened and lightened to 294 lbs but were still too heavy as the maximum load a mule could be expected to carry was nearer 200 lbs.
In 1865 the first RML mountain gun was introduced. It was the 7-pr (3-inch) 2-cwt Mark 1, made by boring out and rifling old SBML bronze pieces on the Woolwich pattern with a twist of one turn in 20 calibres. As this gun was considered too heavy a Mark 2 of 200 lbs was produced by having the exterior turned plain, ie by removing the old decorative mouldings and by shorteneing the bore by two inches. About 50 were made but it was not introduced into the service because the preponderance was not considered satisfactory. Of those made, some were taken by the RN as boat guns, while six were sent to Canada in 1870 for the Red River expedition.
In 1865 five 7-pr (3-inch) Mark 1 steel guns of 190 lbs were made for India but no more of this pattern eventuated. In 1867 thirteen Mark 2 guns of 150 lbs were made but noo pattern sealed. There followed a Mark 3 of 150 lbs, but not being considered suffiently powerful, was superseded in 1873 by the Mark 4 of 200 lbs with a longer bore.
RML 7-pr (3-inch) 200 lbs Mk 4 gun
Sights were graduated to 12° elevation. All the Marks 1 to 4 guns were made from solid steel ingots, being the first all-steel pieces introduced by Britain. They were rifled in the same way as the bronze guns described above.