RML 2.5 inch Mountain Gun

Ordnance RML 2.5 inch Mountain Gun
Sikh gunners assembling the gun, circa. 1895
Type	Mountain gun
Place of origin	United Kingdom of Great Britain and Ireland
Service history
In service	1879 - 1916
Used by	British Empire British Raj
Wars	Second Boer War World War I
Production history
Designer	Colonel le Mesurier, RA
Designed	1877
Manufacturer	Royal Gun Factory
Specifications
Weight	800 pounds (363 kg) total
Length	69 inches (1,750 mm)
Barrel length	66 inches (1,680 mm)
Shell	7 pounds 6 ounces (3.35 kg) (Shrapnel) 8 pounds 2 ounces (3.69 kg) (Ring)
Calibre	2.5 inches (63.5 mm)
Action	RML
Muzzle velocity	1,436 feet per second (438 m/s)
Maximum firing range	3,300 yards (3,018 m) (shrapnel) 4,000 yards (3,658 m) (ring)

The Ordnance RML 2.5 inch mountain gun was a British rifled muzzle-loading mountain gun of the late 19th century designed to be broken down into four loads for carrying by man or mule. It was primarily used by the Indian Army.

It was intended as a more powerful successor to the RML 7 pounder Mountain Gun. Some writers incorrectly refer to the 2.5 inch gun as a "7 pounder" because it also fired a shell of approximately 7 pounds, but its official nomenclature was 2.5 inch RML.

In 1877 Colonel Frederick Le Mesurier of the Royal Artillery proposed a gun in 2 parts which would be screwed together. The Elswick Ordnance Company made 12 Mk I guns based on his design and they were trialled in Afghanistan in 1879. Trials were successful and Mk II with some internal differences made by the Royal Gun Factory entered service.

The gun was a rifled muzzle-loader. Gun and carriage were designed to be broken down into their basic parts so they could be transported by pack animals (4 mules) or men. The barrel and breech were carried separately, and screwed together for action, hence the name "screw gun".

The gun was used in the Second Boer War (1899–1902) on its standard mountain gun carriage, and also with the Natal Field Battery at Elandslaagte and Diamond Fields Artillery at Kimberley on field carriages which had larger wheels and gave greater mobility.

A major defect in the war was that the gun's cartridges still used gunpowder as a propellant, despite the fact that smokeless cordite had been introduced in 1892. The gunpowder generated a white cloud on firing, and as the gun could only be aimed using direct line of sight, this made the gunners easy targets for Boer marksmen as the gun lacked a shield.

It proved to be ineffectual and outclassed by Boer ordnance and was replaced by the BL 10 pounder Mountain Gun from 1901.

Either 4 or 6 guns (sources appear imprecise) were returned to service from Southern African garrisons in 1916 and were employed by the Nyasaland-Rhodesian Field Force in the campaign in German East Africa. Writers who refer to "7 pounders" in World War I are in fact referring to this 2.5-inch (64 mm) gun.