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| Armour-piercing, capped, ballistic capped shell |
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 Cross section of an APCBC shell (APHECBC) |
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Armour-piercing, capped, ballistic capped (APCBC) is a type of configuration forarmour-piercing ammunition introduced in the 1930s to improve the armour-piercing capabilities of bothnaval andanti-tank guns. The configuration consists of anarmour-piercing shell fitted with a stubbyarmour-piercing cap (AP cap) for improved penetration properties againstsurface hardened armour, especially at high impact angles,[1] and an aerodynamicballistic cap on top of the AP cap to correct for the poorer aerodynamics, especially higher drag, otherwise created by the stubby AP cap.[2] These features allow APCBC shells to retain higher velocities and to deliver more energy to the target on impact, especially at long range when compared to uncapped shells.
The configuration is used on both inert and explosive armour-piercing shell types:[2]
The APCBC configuration is an evolution of the earlier APC configuration (armour-piercing, capped), itself an evolution of the simple AP configuration (armour-piercing, uncapped). The APCBC configuration is however expensive and thus a large amount of both historical and modern armour-piercing ammunition uses only one of the two caps: APC (armour-piercing, capped) and APBC (armour-piercing, ballistic capped).
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| AP | APC | APBC | APCBC |
|---|---|---|---|
 |  |  |  |
Projectile body | Projectile body Armour-piercing cap | Projectile body Ballistic cap | Projectile body Armour-piercing cap Ballistic cap |
| Uncapped | Capped | Ballistic capped | Capped, ballistic capped |
By 1910 it was well-established that the aerodynamically optimal form of a solid projectile does not lend itself to best-attainable armour penetration, and remedies were devised.[3]
Aballistic cap (BC) is a hollow thin-walled aerodynamically shaped metalcone mounted on the top of a projectile to cover it with a more aerodynamically efficient shape. This reduces drag in flight, so highervelocity and hence range is obtained giving better penetration over longer distances. On impact, the ballistic cap will break off or collapse without affecting the impact performance of the armour-piercing cap and penetrator.[2]
Ballistic caps are used on a great variety of projectiles other than APCBC shells and exist to allow the projectile or cap underneath to have a less aerodynamic shape more suitable for the effect of the munition. They are most often fitted by pressing the edges of the cone into a groove around the edge of the projectile or AP cap.[2]
The primary job of anarmour-piercing cap (AP cap, most often shortened tocap) is to protect the tip of the penetrator on impact, which could otherwise shatter and not penetrate.[2] It consists of a metal cap, often solid in structure, which is mounted on top of the projectile lying against the tip. Depending on the purpose of the cap, different designs exist. Among other things, the cap can be made of soft metal (soft cap), or hard metal (hard cap).[2]
Early World War II-era uncapped AP projectiles fired from high-velocity guns were able to penetrate about twice their calibre at close range: 100 m (110 yd). At longer ranges (500–1,000 m), this dropped to 1.5–1.1 calibres due to the poor ballistic shape and higher drag of the smaller-diameter early projectiles.
As the war progressed, vehicle armour became progressively thicker (and sloped) and early war AP and APHE were less effective against newer tanks. The initial response was to compensate by increased muzzle velocities in newly developed anti-tank guns. However, it was found that steel shot tended to shatter on impact at velocities greater than 823 m/s (2700 feet/second).[4]
To counter this, a cap of softer metal was attached to the tip of an AP (solid) round. The cap transferred energy from the tip of the shell to the sides of the projectile, thereby helping to reduce shattering. In addition, the cap appeared to improve penetration of sloped armour by deforming, spreading, and "sticking" to the armour on impact and thereby reducing the tendency of the shell to deflect at an angle. However, the cap structure of the APC shell reduced the aerodynamic efficiency of the round with a resultant reduction in accuracy and range.[4]
Later in the conflict, APCBCs fired at close range from large-calibre, high-velocity guns (75–128 mm) were able to penetrate much greater thicknesses of armour in relation to their calibres (2.5 times) and also greater thicknesses (2–1.75 times) at longer ranges (1,500–2,000 m). Comparative testing of British17-pounder (76 mm) gun and US Army APCBC rounds fired into captured GermanPanther tanks indicated the APCBC munitions were more accurate than late wararmour-piercing discarding sabot (APDS) shot, though the lot used was described as sub-standard and the report made no determination of general APDS accuracy.[5]
APCBC shot was produced for a wide range of anti-tank artillery ranging from 2-pounders to the German 88 mm. This type of munition was also designated as APBC (armour piercing ballistic capped), in reference to the Soviet version of APCBC. APCBC shot was also used in naval armaments in World War II. After World War II, the trend in armour-piercing munitions development centred on sub-calibre projectiles. No tank guns designed since the late 1950s have used full-caliber AP, APC, or APCBC ammunition.[6]