#7 or bird shot would not even scratch the paint if falling under gravity. It is approximately 0.1 gram. If you ever see what it looks like in real life, it is tiny and soft. The only reason it does damage is because the charge gets it going at a fair speed (which is loses very quickly).
Since you seem to have experience here, what do you think the lightest shot that would damage a midsize drone (ie DJI phantom) at a useful range would be?