Take a .50 BMG or a 20MM and make some of those blue CCI shot holders for them and fill them with some #4.
That isn't nearly as portable, but we can certainly talk about it for longer ranges. I still like the shot gun as something easy to hand to troops with range and reach. IMO, something like a goose gun might be better (or at least a shotgun with longish range capability). I wonder how well the military's Beneli M4s would do with heavier shot.
I did see a video on a test vehicle for 30 or 40 mm explosive rounds fired from an anti-air armored vehicle. Looks like a cool concept especially for the intermediate sized drones. Might be a little big for the smaller drones. And I am not certain if the radar can detect the smaller drones effectively.
Dumb Question: If a drone is broadcasting video back to its operator, can the radio emissions be tracked? I am sure it is not easy and if the drones stay low to the ground, much harder.