Could we skip the "knock down" nonsense, please?

Even multiple 7.62 GPMG hits do not 100% ensure that a man doesn't return fire any more.

Most lethal pistol hits are lethal because of bleeding, and no matter how big the hole in your leg or stomach, it cannot drain the blood from your arm instantly.

The only thing that instantly kills is a hit to the central nervous system (including brain). Additionally, cutting the bone and/or nerve bundle in a leg drops a man and cutting the same in the weapon-wielding arm keeps him from returning fire.
All else is unreliable.