What type of device is manufactured to discharge a bullet using compressed gas and is classified as less than 5.6mm?

The correct answer is an airgun. Airguns are specifically designed to discharge a projectile, such as a pellet or BB, by using compressed gas to propel it. This type of firearm operates differently from traditional firearms, which use gunpowder as the propellant. Airguns can deliver projectiles at relatively high speeds while maintaining a caliber that is usually less than 5.6mm, making them suitable for sport shooting, target practice, and small game hunting.

Other types of devices listed in the question either do not use compressed gas or do not meet the specified caliber criterion. For instance, shotguns typically utilize larger shells and are used for shooting at a range typically greater than 5.6mm. Recoilless guns are designed for launching larger projectiles, often in military applications, and also exceed the 5.6mm threshold. Flare guns, while they may use compressed gas for firing flares, are not classified under the same categories as firearms used for shooting bullets and usually discharge flares for signaling rather than for projectile impact. Therefore, airguns clearly fall into the category specified in the question.