Being gun people, we tend to think "how would I use my gun?"
Yet, in the Palm Bay massacre in 1987, IIRC the hero of the day was a guy who used not a gun, but a pickup truck. He picked up wounded, and used his vehicle like an APC, letting some on foot use it as moving cover between them and William Cruse as they retreated.
Assisting others in a crisis may not require violence; there may be non-violent good that can be accomplished, depending on what we consider to be acceptable levels of risk.
My personal level of acceptable risk is reasonably high, based on my long-term career (military aviation as active officer and/or contractor), but it would be significantly reduced if I were with my wife and unborn son.
That said, if on my own or with an armed friend, and I had a clear shot at a positively identified BG, I would feel a duty to take the shot.