.55 Boys (13.9x99mmB) is an anti-tank cartridge developed by United Kingdom in 1930s, it designed for Boys anti-tank rifle, which used by United Kingdom and some Allied forces in WW2.
The concept was influenced by German 13.2x92mm SR TuF (Tank und Flieger, lit. tank and aircraft), which designed for Tankgewehr M1918 anti-tank rifle in WW1. Captain H.C Boys, who have design a new cartridge by necked up .50 BMG(Browning Machine Gun, 12.7x99mm) cartridge. Belt also added on the cartridge case, prevents it accidentally chambered in .50 BMG firearms. It was adopted and produced with Boys Anti-Tank rifle in 1937, shortly before the WW2 started (1939).
This model was ideal for history reenactment, movie props, collectibles items or teaching models.
The dimension of this dummy cartridge was based on technical drawing and data that found on the internet, includes detail measurement. However, the dimension may vary from original one due to tolerance.