Hand written Vertical Interval graph for Mk VIIIz .303 ammunition : 2/2 Australian Machine Gun Battalion

V I (Vertical Interval) graph, hand written in black ink on lambskin, for Mk VIIIz .303 ammunition. The graph has a title panel which reads 'V.I. Graph. 0.8.85 John C Cockram', and is graduated up the left hand side in yards, from 1000 to 4500. The graduation along the top is tangent angle, (the angle of the gun above horizontal required for a given range) and is marked from 0 to 10 degrees. Further graduations along the bottom of the graph read from zero to 600.

When Mk VIIIz ammunition was first issued to machine gun units in the Middle East in 1942, no range tables or slide rules were issued to accompany it. 2/2 Australian Machine Gun Battalion, faced with this problem, set out to devise its own tables, and two Sergeants of A Company, John Cockram and Gus Longhurst, undertook the task. Eventually their calculations were completed and, in the absence of suitable heavy-duty paper, were copied onto a lambskin which Cockram had acquired in Beirut to have made into a gift. The new tables proved entirely successful, and were later used by the battalion during the fighting at El Alamein, enabling accurate indirect fire to be delivered at ranges of over 3600 yards. Mk VIII .303 ball ammunition was a streamlined and boat-tailed development allowing greater range through improved ballistic design. Mk VIII was propelled by cordite, but the more powerful MkVIIIz, propelled by nitro-cellulose, increased useful range to 4500 yards, and muzzle velocity to 2500 feet per second. The creation of the tables is described on page 86 of the 2/2 Australian Machine Gun Battalion's history, 'Muzzle Blast', which also features a photograph of the V I Graph.