flak guns are still around, it's airburst ammunition.  looks like most recently a new flak shell was put into production 2008ish for the mk44 bushmaster 2 cannon which is used by the singapore army, the kto rosomak in polish service, and the cv90 afvs in finnish, norwegian the swiss and united states on various vehicles and ships. the korean bulpup s&t daewoo k11 daw has an airburst round, there are a few other rifles that have airburst rounds. any of these would work great against drones. orbital atk a weapons manufacturer who made some of them is about a mile from my old apartment, they are in usa but got bought by china a few years ago but still produce and r&d military research for the usa
United States