.55 inch Boys Armour Piercing
Armour-Piercing
Although the trials had found the 800 grain armour-piercing bullet satisfactory, when the calibre of the Boys was increased to .55 inch the bullet weight was increased to 930 grains to meet the improvements that had occurred in AFV armour.
"Cartridge S.A. Armour Piercing .55 inch W Mark I" was approved in December 1936 and shown in LoC paragraph B.2245 of February 1939 to Design DD/L/7416.
Early .production did not show the Mark number but included the Design Number "7416A W" in the headstamp. Contrary to what has been stated elsewhere, this does not represent an Armstrong Whitworth number. It is in fact the Design Department number, more fully "DD/L/7416A" with the addition of "W" to indicate armour-piercing.
The W Mark I had a flat based bullet hardened steel core and two cannelures in the cupro-nickel envelope. Bullet weight was 930 grains of which the core weighed 570 grains. The propellant charge was 186 grains of Cordite MDT 7-2 and muzzle velocity was 2,450 feet per second. The primer annulus was green and included the code "W.I".
The armour piercing requirement was that seven out of ten bullets should penetrate 16mm armour plate at 100 yards at a normal angleof attack. This was less that the original requirement so an improved round with a lighter bullet but considerably higher velocity was introduced.
It was shown as obsolescent in December 1939.
"Cartridge S.A. Armour Piercing .55 inch W Mark II" was approved in June 1939 and shown in LoC Paragraph B.3058 of December 1939. it was to design DD/L/8381 (later superceded by Design DD/L/14009) and differed from the W Mark I in having a shorter bullet weighing 735 grains with a charge of 212 grains of Cordite MDT 7-2. The bullet had a cupro-nickel clad steel envelope with a hardened steel core weighing 445 grains in a lead/antimony sheath.
Velocity was increased to 2,900 feet per second and penetration proof was increase to seven out of ten bullets should penetrate 19mm of armour at 100 yards at 20 degrees angle of attack.
Ignore this picture as it is only there for layout purposes
Left to right: Early AP "K37 7416A W", W Mark I "K39 WI", W Mark II "K1942 WII", Canadian W Mark II "DAC WII 42"
Left: Label for .55 inch Boys Armour Piercing W Mark I
Composite Rigid
By 1940 the Boys rifle was ineffective against the latest German tanks and even the improved W Mark II was completely outclassed by their armour. The Boys rifle was still effective against thin skinned vehicles and against the lighter armoured Italian and Japanese tanks. by 1942 thought was therefore given to improving the performance by use of a saboted projectile.A composite rigid bullet was designed that had a sub-calibre tungsten steel penetrator, the rear half of which was supported in a full calibre aluminium sabot. The forward part of the penetrator was covered by a windshield to give a more normal bullet profile. The joint between the windshield and the sabot was unusual in that instead of a straight line there were four hemispherical cut-outs on the sabot.
Two types are known, one with a black Bakelite windshield and the other with an aluminium windshiled. Normal W Mark II cases were used.
(Left) Composite rigid projectile with aluminium windshield headstamped "K43 WII" and (right) with Bakelite windshield headstamped "RG 42 WII".