When serving in the Finnish Army in mid 70s (shortly after Vietnam War) we were trained to use our assault rifles against a/c and helicopters. A squad would fire together a short burst following orders of the squad leader who would give the nature of the target, its flight direction and the amount of the lead and then order "Fire". We were not suppose to fire at oncoming aircrafts or attack helicopters but at those flying past us.
During the WWII Finnish light AA batteries had also two? twin rifle calibre AA mgs, in 1944 they were used to fire departing Il-2s in order to kill the rear-gunners.