Why smart ammunition favors 40 mm over 30 mm

Could 30 mm guns become the economical smart-ammunition answer to drones?

Possibly, but 40 mm has so far offered a more practical size for cost-effective guided or programmable ammunition.

The exchange considers guns as a lower-cost answer to drones and other numerous threats. Navies have spent years trying to shrink smart-projectile technology below 40 mm. The smaller 30 mm shell leaves less room for the required components, making the desired effect harder to achieve economically. Calibre therefore affects range, destructive power, and whether advanced ammunition can be manufactured at a useful price.