.55 Boys

.55 Boys
Type	Anti-tank rifle cartridge
Place of origin	United Kingdom
Service history
In service	1937–1945
Used by	United Kingdom Commonwealth of Nations Finland, et al.
Wars	WWII Winter War Continuation War
Production history
Designed	1937
Manufacturer	Kynoch
Specifications
Parent case	.50 BMG
Bullet diameter	14.30 mm (.565 in)
Neck diameter	15.392 mm (.606 in)
Shoulder diameter	15.34 mm (.604 in)
Base diameter	20.168 mm (.794 in)
Rim diameter	20.244 mm (.797 in)
Rim thickness	2.44 mm (.096 in)
Case length	97.79 mm (3.85 in)
Overall length	133.43 mm (5.253 in)
Ballistic performance
Bullet mass/type Velocity Energy 946 gr (61 g) Mark I 760 m/s (2,500 ft/s) 17,726 J (13,074 ft⋅lbf) 741 gr (48 g) APCR Tungsten 945 m/s (3,100 ft/s) 21,434 J (15,809 ft⋅lbf)
Test barrel length: 914.4 mm (36 inches) Source(s): Ammo Encyclopedia, 2nd Edition by Michael Bussard

The .55 Boys (13.9×99mmB in metric) is an anti-tank cartridge used by the United Kingdom in World War II. It was designed for use with the Boys Anti-Tank Rifle.

Design

The .55 Boys is a 13.2×99mm Hotchkiss cartridge necked up to accept a .55 caliber bullet in mid-1930s. Since the shoulder of the case was narrowed, a belt was added to ensure reliably correct headspace. It performed poorly when compared to contemporary foreign anti-tank rounds, such as the German 7.92×94mm Patronen and the Soviet 14.5×114mm rounds and, as a result, it was quickly deemed obsolete.

History

.A 55 Boys cartridge (left) and a .50 BMG cartridge (right).

The concept of a small arm round for use against tanks began with the German 13.2mm TuF round, designed during World War I for use against the first British tanks.

In the 1930s, the United Kingdom began designing an anti-tank rifle to counter enemy armoured vehicles in the event of a war.

Initially the gun design was trialled using .50 inch bullet with a belted case due to lack of armour-piercing performance the calibre was increased to .55

Development on what is known as the .55 Boys was started by Captain Henry C. Boys, the Assistant Superintendent of Design at the Royal Small Arms Factory, Enfield in 1934. Boys died before the rifle was officially adopted and it was named after him. The .55 Boys round was a modified .50 BMG round necked up to accept a larger, steel-cored bullet in order to increase its armour penetration. A belt was added to reinforce the case with the heavy propellant charge.

The .55 Boys was adopted and manufactured alongside the Boys Anti-Tank Rifle in 1937 throughout the Commonwealth of Nations by firms such as Kynoch. However, when the United Kingdom entered World War II, the .55 Boys round was soon found to be insufficient against even early war Axis tanks in late 1939 and 1940. However, the United Kingdom had to rely on the .55 Boys round for because no better infantry anti-tank weapons were available. When the PIAT anti-tank weapon was introduced in 1943, the shaped charges it fired were far more effective against enemy armour than the .55 Boys round had been. The Boys rifle was phased out of service on the frontline as the PIAT became the British military's primary handheld anti-tank weapon.

Although not effective as an anti-tank weapon, the .55 Boys was used until the end of World War II by British and Commonwealth countries. It also saw use during the Winter War and Continuation War by Finland. The Boys was issued to Home Guard units in the UK for use against "light armoured fighting vehicles...which the Home Guard are likely to have to deal with, certainly in the early stages of either an air-borne or sea-borne landing on our coasts." A handbook for its use noted that as well as the expected penetration of armour at various distances and angles that it would penetrate 14 inches of brick wall and 10 inches of sandbags.

By the conclusion of World War II, the .55 Boys was no longer used in any major capacity.

Variants

The .55 Boys round went through two major variants in its lifetime, along with an experimental variant that was never adopted by the United Kingdom.

Mark I

This is the first variant of the .55 Boys. It uses a 926 gr (60.0 g). hardened steel core bullet with a lead sleeve, which is covered with a steel jacket. A ball and tracer version of this round was also created along with a practice round using an aluminum core in order to be more feasible for training. It has a muzzle velocity of roughly 747 m/s (2,450 ft/s).

Mark II

An improved loading named the Mark II was released in order to increase the round's velocity and its penetration. It generates a muzzle velocity of approximately 884 m/s (2,899.5 ft/s).

At an ideal angle, the Mark 2 round was able to pierce 0.91 inches (23.2 mm) of armour at 100 yd (91 m), 0.82 inches (20.9 mm) at 300 yards (270 m) and 0.74 inches (18.8 mm) at 500 yards (460 m).

APCR tungsten round

An experimental armour-piercing composite rigid (APCR) .55 Boys round was designed in 1942. It used a tungsten core instead of a steel core, which greatly increased its penetrating ability and gave a boost to its muzzle velocity from the Mark II's 884 m/s to approximately 944 m/s (3100 ft/s). It differs from the Mark I and II rounds because of its two-part bullet. This model was never officially adopted because far better anti-tank rounds and weapons, such as the PIAT, were entering service at the time. The .55 Boys, even with a greatly improved bullet, was simply too weak to defeat the tanks being fielded by the Axis powers.

See also

• 13mm caliber
• 14.5x115mm
• 12.7×108mm
• List of rifle cartridges