Logo from Scott Cunningham.

Types of Ammunition

Sub-calibre Ammunition Part 1 General Design

lthough the various refinements made a significant contribution to the performance of APBC, APC and APCBC projectiles, their ability to defeat increasingly thick armour came principally from increases in their muzzle velocity and calibre. However a practical limit was reached when the calibre rose to around 120mm, because larger calibre rounds were too heavy for loaders to handle, and when the muzzle velocity rose to around 1,000m/s because of the high rate of bore wear. In consequence, the c.200mm penetration at 30° of the German P.J.K.80 in the Jagtiger represented the limit of what could be achieved with full calibre armour piercing ammunition fired from manually loaded guns.⁷

Several types of sub-calibre ammunition were developed. They all have in common a projectile design consisting of a hard, high density sub-calibre core within a light alloy body. Most of the kinetic energy imparted to the projectile is concentrated in the sub-calibre core and hence on a smaller area of the target. This, together with the higher density of the core, leads to significantly greater armour penetration than that achieved with full calibre projectiles fired from the same gun.⁷

Penetrators are usually made from tungsten and are very, very hard.

Early sub-calibre cores or penetrators are usually made from tungsten carbide sintered using nickel or cobalt as the bonding agent or binder. Its main advantage is its high density, ranging from 14.3g/cc to 16.3g/cc compared with 7.85g/cc for steel (and 1g/cc for water); and also its high hardness, ranging from 900 to 1,800 VDH compared with 850 VDH (about 739 BHN, the highest BHN possible) for hardened shot steel.⁷ Tungsten carbide has a high compressive strength and is two to three times as rigid as steel. Its high wear resistance makes it particularly useful as a cutting surface for machine tools. Industrial use was so important that when Germany was cut off from tungsten supplies the production of sub-calibre cores ceased and over half of the existing stockpiles were put into storage for future industrial use.

Tungsten carbide is relatively brittle and as a result penetrators made of it break up as they pierce armour, creating a highly lethal spray of particles. However this brittleness also causes them to fracture when they strike armour obliquely, so that their armour piercing performance falls off appreciably as the slope of the target armour increases.⁷ Against spaced armour the penetrator invariably breaks up completely after passing through the first plate, and the fragments tend to disperse before striking the second plate. This can be reduced but not eliminated by sheathing the core with steel, but this was only done by Britain in World War II.¹

Krupp experimented with tungsten cores from 1929 and limited production of such cores for infantry ammunition began in 1933. Krupp emphasised high density as the key requirement for the core, resulting in a high proportion of tungsten, but found that for cores of 15mm diameter and larger tungsten carbide sintered using nickel was needed to increase toughness and reduce the tendency to shatter. A typical German core has 93% tungsten, 5% carbon and 1% nickel.⁸

German requirements for the hardness of cores were 1,725–1,800 VDH for cores used in guns up to 50mm, and 1,410–1,460 VDH for cores used in larger guns. Actual hardness measured by the USA of smaller cores averaged 1,365 VDH. German cores were 34–43% of the diameter of the gun calibre, with later versions of ammunition tending to increase the percentage ratio to improve penetration:⁸

For the source of data see endnote 8.

Soviet cores were also high in tungsten content, but to save on its use their 76mm projectile had a two piece core, with the forward part of tungsten and the rear part of nickel. The core’s lesser weight understandably reduced its penetration. A typical Soviet core has 89% tungsten, 6% carbon and 4% nickel, has a hardness of 900–1,200 VDH and is 36% of the diameter of the gun calibre.⁸

The British stressed toughness over density in the design of their cores. Thus the proportion of tungsten was reduced, and cobalt was used instead of nickel as a bonding agent. British research indicated that 50% of the gun calibre was a better size for the core diameter, and all British cores were sheathed in steel to reduce shatter against spaced armour and highly oblique targets. A typical British core has 82% tungsten, 5% carbon and 12% cobalt, has a hardness of 1,150–1,400 VDH⁸ and is 45–50% of the diameter of the gun calibre:⁹

For the source of data see endnote 9.

The USA had the advantage of studying British and German designs, but their own sub-calibre projectiles entered the war too late to have any effect. USA design stressed toughness over density, similar to the British requirements, but used pure tungsten instead of tungsten carbide and did not sheath the core in steel. A typical USA core has 88% tungsten and 12% cobalt, has a hardness of 1,000–1,200 VDH and is 50% of the diameter of the gun calibre.⁸

Sub-calibre Ammunition Part 2 APCR

Do you like this web site? Please rate it between one and ten, with ten being the best:

Ratings are submitted to: The Wargames and Military History Search Engine.