Why 40 mm can suit close defence better than 57 mm

Why choose a 40 mm close-defence gun instead of a larger 57 mm weapon?

Forty millimetres offers greater ammunition capacity while still supporting effective smart or programmable rounds, a useful balance for repeated terminal engagements.

The calibre choice is driven by the defensive job rather than a simple preference for the largest projectile. A 40 mm mounting can carry substantially more ready ammunition than a 57 mm system, which matters against repeated close-range attacks. Modern guided or programmable effects are also practical at 40 mm, allowing bursts to create a fragmentation pattern as well as direct hits. Going smaller may make sophisticated ammunition disproportionately expensive or reduce terminal effect. Magazine depth, the expected number of engagements, and munition technology therefore shape a close-defence gun choice.