Well Morpheus,As a 99 yr old Englishman, you probably saw action in WWII. I am much younger, but I saw action in the Kenya Emergency, and a sergeant major explained this issue of causality in simple terms that even I could understand. Most of us had never seen action, and our first casualties caused the usual reaction, so he made sure that we knew where Our Duty lay.
Briefly, he pointed out that while "The Yanks" put great stock in having their soldiers wounded and even gave them a medal for it, Her Majesty's Army frowned on this practice, because it was expensive and created a lot of paper work. Therefore, no soldier was to get himself wounded or killed without specific orders from his commanding officer. "Do I make myself crystal clear?"
So both the necessary and efficient cause of death from a gun shot is not the shooter, the gun or the bullet, or even secondary infection, but the poor sod who carelessly allows himself to be shot.
Hope this helps.