Piercing Caps

t an early stage in World War II the phenomenon of “shatter” was encountered. The term is applied when a projectile failure occurs at high impact velocities, with its complete collapse. At lower velocities against the same target plate normal penetration may occur without any projectile break-up.¹ As the velocity increases the projectile shatters and fails to penetrate. As velocity increases still further the shattered pieces can once again penetrate the target plate. The band of velocities between the onset of shatter failure and the point at which penetration again occurs (this time by the shattered pieces) is called the “shatter gap”. In the case of the British 2–pounder gun this gap occurs at normal combat ranges.³

A cutaway of an APCBC/HE projectile. The thin ballistic cap is at the right of the picture, over the piercing cap which is in dark grey protecting the tip of the shell body. The small cavity at the rear is contains HE. From the Russian Military Zone.

Shatter is mostly eliminated by adding hard steel piercing caps to the nose of the projectile. This directs the impact shock away from the tip of the shell to the shoulders, preventing the tip from shattering at high impact velocities, and the projectile is called an APC (armour piercing capped) projectile. APC allows FH armour, and thicker slabs of overmatching homogeneous armour, to be defeated without the shattering of the projectile.² Often a ballistic cap is fitted over the piercing cap to improve flight characteristics and the round is then referred to as an APCBC (armour piercing capped with ballistic cap) projectile.

USA ammunition nomenclature in World War II did not recognise the addition of a ballistic cap, so it rather confusingly uses “APC” for an APCBC projectile.

“Use of a piercing cap does not guarantee that the projectile will not shatter.”

Use of a piercing cap does not guarantee that the projectile will not shatter. In the case of the USA 76mm M1 gun firing an M62 APCBC projectile the shatter gap occurs between about 200m and 1200m, when the target plate is around 100mm thick and hard, such as typical German vehicle armour. That is why the USA 76mm M1 gun was a Tiger I killer on the charts, but not in real life. When it was fired in tests it tended not to shatter because USA test plate was somewhat soft, so the shatter gap was not revealed by the USA testing and development program.³

USA piercing caps were relatively soft, while British and German caps were as hard as the projectile itself, usually 59–67 on the Rockwell C scale (634 to >739 BHN). The effectiveness of different piercing caps, or the lack of them, can be shown by firing tests where each projectile impacts the target plate at the same velocity, eliminating the effect of different muzzle velocities. This was done by the British firing 75–76mm calibre projectiles from different nations against I.T.80 plate (255–302 BHN) at an impact velocity of 610m/s:⁴

USA ballistic caps caused flight instabilities, yawing up to 15° and thus increasing the striking angle and reducing penetration.⁴ It is possible that ballistic caps of other nations would also have had this problem, but it may not have been detected in tests or otherwise remarked upon.

Britain, Germany and the USA used APCBC projectiles as their standard anti-tank ammunition during World War II. The Soviet Union did not field APC or APCBC projectiles until the 1950s. They certainly were capable of doing so earlier, but perhaps the crisis in World War II was too great to allow mass production of such a complex round.²

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Types of Ammunition

Piercing Caps