It doesn’t take a 50 to bring down a chopper.
A bow and arrow with several hundred yards of fine kevlar and a small weight works fine. How long will a helicopter fly with locked controls?
When I was flying low level & doing nap of the earth iterations, our worst nightmare was a wire strike. Even a small power line could foul the main rotors & bring it down chop-chop. Harder to spot than the big wires.
And much less than a .50 cal can destroy a tail rotor gearbox or make it run dry & then seize.
HVAC guy was here yesterday. His Dad flew Cobras in VN & had two shot down. I flew Hueys and was more fortunate.
Helicopters have always been vulnerable to small arms fire especially in slow flight.
And a few yards of barbed wire and some cinder blocks will pull the tread from a tank. With no tread a tank is a pillbox. A pill box with no infantry is a tomb.