Re: machine gun?
Older machine guns tended to have heavier rounds which are more of a nuisance to innocent bystanders.
However perhaps a modern equivalent of the WW2 Sten (a 9mm sub machine gun) fitted to a tripod allowing no less than a 70 degree angle of fire loaded with a suppressor and (tracer) hollow point rounds (to reduce range and kinetic energy) keeping the firing arc within the airport's perimeter, of course it would have to be fired away from buildings/aircraft. It would be terribly inaccurate but I'm sure it would be accurate enough, in the right hands, to hit a commercial drone at the typical service ceiling of 400-500ft. I'd be more than surprised if a 9mm hollow point fired at a 70 degree angle from a sub machine gun/pistol could make it much further than a kilometre.
It wouldn't be terribly difficult to incorporate a laser range-finder/target illuminator.