| Metric (mm) | Imperial (in) | |
| Calibre | 13.9 x 99 | .55 |
| Name: | Boys | |
| Case Type: | Belted, bottlenecked | |
| Bullet Diameter: | 14.30 | |
| Case Length: | 99.1 | |
| Rim Diameter: | 20.26 | |
| Neck Diameter: | 15.39 | |
| Shoulder Diameter: | ||
| Base Diameter: | 20.27 | |
| Total Length: | 133.9 | |
| Weight: | 125 grammes | |
| Primer: | Berdan | |
| Year Introduced: | 1937 | |
| Also known as: |
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| United Kingdom (Experimental) |