In the US, it depends on the jurisdiction because each state has its own homicide statutes: but, the defining elements don't differ a lot. Drawing on Washington state law, the first question is whether you intended to kill a person (it doesn't have to be a specific person). If you did, you have committed first-degree murder. It is first-degree murder, because it requires a certain amount of advance planning to kill with a drone. It does not matter that the drone houses the gun that killed the person and a program determines when the gun fires (the "it was the drone, not me" defense gets you nowhere: otherwise, you could always claim "It wasn't me, it was my gun / knife / fist".)
If instead this is a badly-designed pig-slaughtering drone, then it could be manslaughter in the first degree, if the act was reckless, or manslaughter in the second degree, if the act was with criminal negligence. To determine which it is, you look at the definitions:
A person is reckless or acts recklessly when he or she knows of and
disregards a substantial risk that a wrongful act may occur and his or
her disregard of such substantial risk is a gross deviation from
conduct that a reasonable person would exercise in the same situation.
A person is criminally negligent or acts with criminal negligence when
he or she fails to be aware of a substantial risk that a wrongful act
may occur and his or her failure to be aware of such substantial risk
constitutes a gross deviation from the standard of care that a
reasonable person would exercise in the same situation.
So it would depend on whether you decided that safeguards which would prevent shooting people were too much bother (you know there is a risk and set aside that concern), or it didn't occur to you that a flying gun might hurt a person.