If you're going to use an AR, I would suggest something very lite and frangible, such as a varmint bullet. Probably better would be a shotgun with 7 or 7 1/2 shot, since just about any damage to a drone, especially in a motor or propeller, will make it crash.
Before you go shooting at a drone be aware that shooting at any mechanical flying machine can bring the wrath of the FAA upon your head very quickly. Always be aware that the majority of drones are carrying camera equipment on board, which can make it easy to identify the shooter. Even if a drone is flying over your house it might not be breaking any laws, although personally, if it's within shotgun range it's too close for me! About the only thing you can do is call local law enforcement and/or the FAA and hope they can identify the operator. All drones over a certain weight must have a means of remotely identifying the drone and pilot. Of course, if they are flying illegally, catching the operator can be difficult, at best. I don't believe anyone can give you permission to shoot at a drone. While the government supposedly has tech that can jam a drones radio signals, if it's preprogrammed to fly a specific pattern and isn't under the direct control of an operator, that might prove useless.
About the only way to fight back is to call the FAA & local law enforcement and whine loudly. I suppose you could get a laser pointer snd try to blind it's camera (if you think it's spying on you) but that could prove difficult depending on the range.
Best bet is to call it in and then ignore it. Or moon it, maybe! Not a lot of choices, unfortunately.
Cheers,
crkckr