Assault is scaring innocent people intentionally. Battery is hitting innocent people intentionally.
Murder is intentionally shedding innocent blood.
All of these acts create a state of nature called war.
Self-Defense is the act of intentionally inflicting assault, battery and death on those who attack the innocent with assault, battery and murder.
Inanimate objects have no capability to intentionally do anything. The actions of the perpetrator determine the use and character of the weapons involved in an act.
Mass killers use weapons for murder. The actual weapon used is evidence and is identified as the murder weapon.
If you brandish a weapon and point it at someone that is assault. The weapon is identified as the assault weapon.
If you but-stroke someone that is assault and battery. The weapon used is the assault and battery weapon.
There is no general category of assault weapon in the military. All weapons can be used from a defensive or offensive posture to commit assault, battery and killing.
I hope this was helpful.–Gy