What type of projectile is fired from the chain gun?

The correct answer is that a chain gun typically fires 30mm explosive shells. These shells are designed for use in aircraft or vehicle-mounted applications, where high rates of fire and effective impact are critical for delivering firepower against various targets.

The 30mm caliber enables a balance between projectile weight and manageable recoil, allowing for sustained firing while maintaining accuracy and control. The explosive nature of these shells enhances their lethality, making them effective against both soft and hard targets, including personnel and light vehicles.

In contrast, the other choices do not align with the common specifications of chain guns. The 20mm shells mentioned are a smaller caliber and generally used in different weapon systems. The 40mm incendiary rounds and 50mm armor-piercing shells reference calibers that are not standard for chain guns, which are typically associated with larger anti-aircraft or anti-armor systems rather than the rapid-fire capabilities of a chain gun. Therefore, the focus on 30mm explosive shells accurately describes the primary ammunition type used in these systems.