30mm rounds are used specifically in the GAU avenger cannon, mounted in the A10-C Warthog 'tank-buster'. It is designed for anti-armor, and can be fired effectively from about 2 miles away at a given target. The GAU avenger has an auto-correction mechanism which compensates for bullet drop over long distances making them a deadly and accurate ballistic weapon. While they can be used on infantry, they are not designed with this purpose in mind.