Anti-tank rifle cartridge developed for the Boys Mk I anti-tank rifle. Fires a 930-grain steel-core AP bullet at approximately 3,000 fps, generating nearly 20,000 ft-lbs of muzzle energy. Effective against early WWII light armor and armored vehicles.
Type: Rifle
Introduced: 1937, United Kingdom
Parent case: None
Standardization: None
Bullet diameter: 0.55" (13.97 mm)
Case length: 3.899" (99 mm)
Overall length: 4.823" (122.5 mm)
Max pressure: 68,000 PSI
Rim type: Rimless
Primer: Berdan Large Rifle
Typical twist rate: 1:15
Muzzle velocity: 2950–3250 fps
Muzzle energy: 17902–23466 ft-lbs
Effective range: 300 yd
Common bullet weights: 930, 945, 1000 gr
Primary use: Military, Anti-Materiel
Production status: Discontinued
Also known as: .55 Boys ATR · 13.9x99mmB
History: Developed in 1937 for the Boys Antitank Rifle, which entered service with the British Army in 1939. Effective against early German and Italian light armor, the Boys became obsolete as tank armor thickened. It saw extended use against softer targets, APCs, and light vehicles in North Africa and the Pacific. The Canadian Army used the Boys effectively in the Pacific Theater against Japanese light…
Notable firearms: Boys Mk I Antitank Rifle, Boys Mk II Antitank Rifle
Military use: United Kingdom, Canada, Australia, Finland, Poland
Similar cartridges: .50 BMG, 12.7x99mm NATO