"Gunning down" is a phrase that typically refers to using a firearm to kill or injure someone. However, there are several synonyms that can be used to convey the same or a similar meaning. Some of these synonyms include shooting, firing, targeting, taking aim at, laying waste, slaughtering, and assassinating. These words all carry a similar sense of violence and aggression, and can be used to describe actions such as a sniper in warfare, an armed robbery, or a police officer taking down a criminal. Using these synonyms can help writers to convey a sense of danger, urgency, and intensity in their writing.