The proposed flying zone for drones like these is between 60-120m height. Seems like a bullet must travel at least 62m/s to penetrate human skin [1], for which you need a height of at least ~200m [2]. So even dropping a bullet from one the delivery drones would not carry a high risk of fatal injuries.

That, and P=MV, momentum/energy increases proportionally to mass. A 'safe weight' can be defined if the altitude is known.

[1] https://slate.com/news-and-politics/2011/03/can-falling-bull...

[2] https://www.grc.nasa.gov/www/k-12/airplane/mofall.html