Explosive rounds

Posted: Apr 22, 2007 10:23 am Post subject:

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Sorry for the delay, I only have the time to make occasional visits!

The design of effective small-calibre incendiary bullets was difficult. A lot of work was done in WW1, initially for shooting down hydrogen-filled artillery spotting balloons and airships, but they all had disadvantages. The one which the RAF retained into WW2 was the Mk IV (Buckingham) incendiary/tracer, which started to burn on firing and left a smoke trail.

A Belgian, De Wilde, invented what appeared to be a much more effective bullet. I summarise this in the article on the armament of the Battle of Britain fighters on my site:

"The incendiary ammunition was also variable in performance. Comparative British tests of British .303" and German 7.92 mm incendiary ammunition against the self-sealing wing tanks in the Blenheim, also fired from 200 yards (180m) astern, revealed that the .303" B. Mk IV incendiary tracer (based on the First World War Buckingham design – it was ignited on firing and burned on its way to the target) and the 7.92 mm were about equal, each setting the tanks alight with about one in ten shots fired. The B. Mk VI 'De Wilde' incendiary (named after the original Belgian inventor but in fact completely redesigned by Major Dixon), which contained 0.5 grams of SR 365 (a composition including barium nitrate which ignited on impact with the target) was twice as effective as these, scoring one in five.

The 'De Wilde' bullets were first issued in June 1940 and tested operationally in the air battles over Dunkirk. Their improved effectiveness, coupled with the fact that the flash on impact indicated that the shooting was on target, was much appreciated by the fighter pilots. It was at first in short supply, and the initial RAF fighter loading was three guns loaded with ball, two with AP, two with Mk IV incendiary tracer and one with Mk VI incendiary. Another source for the Battle of Britain armament gives four guns with ball, two with AP and two with incendiaries (presumably Mk VI) with four of the last 25 rounds being tracer (presumably Mk IV incendiary/tracer) to tell the pilot he was running out of ammunition. It is not clear why ball was used at all; presumably there was a shortage of the more effective loadings. (By 1942 the standard loading for fixed .303s was half loaded with AP and half with incendiary.)

The Mk VI was good enough that the USA copied it, in simplified form, for both their .30 and .50 aircraft ammo. The British then copied back the simplified design as the Mk VII.

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and armour-piercing cartridges were introduced during 1915. Explosive bullets of the Pomeroy design as Mark VII.Y in 1916.

Several incendiaries were privately developed from 1914 to counter the Zeppelin threat, but none were approved until the Brock design late in 1916 as BIK Mark VII.K [7] Wing Cmdr. Brock RNVR was a member of the Brock fireworks-making family.

These rounds were extensively developed over the years and saw several Mark numbers. The last tracer round introduced into British service was the G Mark 8 in 1945, the last armour-piercing round was the W Mark 1Z in 1945, and the last incendiary round was the B Mark 7 in 1942. Explosive bullets were not produced in the UK after 1933 due to the relatively small amount of explosive that could be contained in the bullet limiting their effectiveness, their role being successfully fulfilled by the use of Mark 6 and 7 incendiary bullets.

In 1935 the .303 O Mark 1 Observing round was introduced for use in machine guns. The bullet to this round was designed to break up with a puff of smoke on impact. The later Mark 6 and 7 incendiary rounds could also be used in this role if required.

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Some effort was made to increase the rate of fire, and a 850 rpm version was apparently perfected, although too late to be adopted.

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