Logo from Scott Cunningham.
Logo from Scott Cunningham.
he second alternative to traditional kinetic energy projectiles was known variously as squeeze bore, taper bore, Littlejohn adaptor, or APCNR (armour piercing composite non-rigid). This improved upon the design of APCR projectiles, but was rarely used during World War II and disappeared shortly afterwards.
The APCNR projectile is fired from a barrel which reduces in calibre, squeezing the relatively soft carrying body around the core so that when it leaves the muzzle its cross sectional is reduced. If the barrel gradually tapers it is called a taper bore; if it reduces in calibre over a relatively small length, with no reduction in calibre elsewhere, it is called a squeeze bore;10 and if it is a squeeze bore attachment to an existing barrel then it is a called a Littlejohn adaptor.
A Littlejohn adaptor for a British 2–pounder gun. Note the gas escape holes down the barrel; earlier versions did not have these but the pressure build up was too great. From the private collection of Chris Shillito.
The advantage of APCNR projectiles is a significantly greater armour penetration, like all sub-calibre projectiles. Since the cross sectional area is reduced during firing, APCNR projectiles do not have the same rapid reduction in velocity and thus penetration with range that APCR projectiles suffer.
The disadvantage of APCNR projectiles is the high rate of barrel wear. Other types of ammunition (such as HE) must be specially constructed to allow them to be fired from the same gun; a conventional projectile of that calibre cannot be used. Like all sub-calibre projectiles using a tungsten carbide core, the core is brittle and breaks up if it strikes the target obliquely or if the target is protected by spaced armour, as described earlier. This was partly overcome by the British in World War II by sheathing the core with steel.1
APCNR was used by Germany until the shortage of tungsten rendered all such weapons useless, since they could not be used with other ammunition. Littlejohn adaptors were used by Britain on the 2–pounder gun, and perhaps also the 37mm gun fitted to M22 Locust during the crossing of the Rhine.
Sub-calibre Ammunition Part 4 APDS
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