Crowded spaces it's a problem, I was more talking to notion of just plain shooting them rather than a use case. A rifle would be dang near impossible, but a scattered spray, you really only need to stop one prop and it's probably on the ground for a standard 4 prop deal. At least mine got real screwy when a blade split mid flight.

Edit: It also could be noted that while a lot of pellets would miss, they would pose a lot less risk that a rifled bullet coming back down. The weight of an individual shot pellet is a fraction of the weight of a bullet, so less momentum, plus the don't have a ballistic spin to maintain their speed that a rifle round does. Basically someone shooting a shot round in the air would come down with about as much force as a handful of gravel once the air resistance slows it a bit.

The optimal sweet spot is probably like 40 meters or something, within 20 or 10 meters and the drone is probably in range to drop a grenade or explode, and becomes much harder to hit because it's capable of making much quicker direction changes relative to where you're standing even as it presents a larger target to you as a consequence of being closer, and a whole lot farther out, and birdshot can't really cut it.

Edit: Oh I was also gonna say, for indoor spaces, it'd maybe be not a good idea even just for hearing protection, but barring that, you could just opt for something lower velocity which you'd probably pack for this occasion if you're defending a set location, and then just load what you need in like 2 seconds. I imagine most drones are going to be flying around above head height anyways, so the main worry would be debris and falloff. You can't prevent debris from the drone really unless you have a net drone or something, and the falloff on the backend of a lower velocity or frangible birdshot with less mass is probably not super consequential except maybe in the case of eye protection. Some sort of ceramic bullet or maybe even steel bbs would probably work without doing too much damage. More than a drone, anyways. It's not as though a drone that rams into another drone is a particularly safe thing, in any case.