Standard hand grenade is roughly 400g / 1 pound; 40mm grenade launcher ammo often is half a pound / 230 grams.

That's considered reasonably effective by the militaries, and fully within the capabilities of many cheap quadcopters.

You don't need a very significant load to blow up a person.

I would like to see Myth Busters like video trying this versus other methods (probably is not legal though). If the target is a bit suspicious then i can't see them waiting for a drone to land on their head before it detonates. From I read on news still idiots with guns commit more terrorist attacks. My intuition is that we will see robot dogs with machine guns mass shootings rather then AI drone dropping a grenade.

I recall videos of quadcopters dropping grenades and mortar rounds (for accuracy - they can drop one within a trench or at the door of a trench-shelter, unlike firing a mortar from distance) as improvised weapons a few years ago in the Ukraine Donbass conflict.

More advanced "loitering munitions" (essentially, drones that fly around until they're sent to slam into a target) were used in the recent Nagorno-Karabakh conflict.

I believe that all these cases were human-in-the-loop for various reasons, but the possibility for automated targeting seems reachable soon if the armies would really want it (which is not certain).

In Syria and Iraq quadrotors with bombs were used pretty extensively, first by ISIL and then later by the Iraqi state. They were used to target small groups of infantry and vehicles [0].

In another case, small CoTS RC planes did significant damage to a Russian airbase in Syria [1].

[0]: Death From Above: The Drone Bombs of the Caliphate https://www.bellingcat.com/news/mena/2017/02/10/death-drone-...

[1]: Russia Offers New Details About Syrian Mass Drone Attack, Now Implies Ukrainian Connection https://www.thedrive.com/the-war-zone/17595/russia-offers-ne...

This big drones also make me anxious, the difference they did not popup on HN or my Youtube, the only drones I seen before today were the ones used for filming. So yeah an AI controlled large done with face recognition and machine guns also gives me chills, I am thinking that at this moment some military dudes are creating strategies to combine the dogs and drones to create a "police" force somewhere.

You don't need a machine gun. If you are using computer aiming and stabilization at close distances, it would almost never miss. A suppressed tube of subsonic .22lr would be quiet, accurate, and very light.