Military ammo were more design to wound than kill right away, a wounded person will, most of the time, slow down/stop 2 others that will attend to their wounded friend.
I first heard this "wounding takes 3 people out of the fight" nonsense as an offered justification for the adoption of the small bore (5.56mm) round for general service use.
And while it seems logical, and actually does happen, sometimes, its not a general truth. It only (sort of) applies when you are fighting an organized army, who fights in the European style. And even then, it doesn't really apply in the manner they imply.
They will tell you that it takes 2 guys to carry the wounded guy off, and so, 3 are out of the fight. It doesn't. Organized armies who place the common European (Western) value on their soldier's individual lives have dedicated medics and stretcher bearers,
who were never part of the fight in the first place. The most you get is wounded soldier (disabling wound, only) out of the fight, and maybe the buddy who watches over him/leads help to him, until the medics get there. This is usually a very short time, and then, the buddy is back in the fight.
Armies who fight in the Asian fashion put a lower priority on helping the wounded, and what effort they expend is more often after the fight.
And rebels/resistance/freedom fighters, what ever version of enemy that isn't set up with an organized medical corps aren't even able to do that. SO, the line about with a wound, you get 3 for 1 is just wishful thinking.
They also don't like to talk about the circular trap that comes with going to a light weight small caliber round. They tell you all about how you can carry more rounds, and so be better off. They don't tell you about how you need more rounds because each individual round isn't as powerful...
The reasons the military still uses FMJ ammunition are simple. First, is the continued lip service to the Hague Accords (often mistakenly referred to as the Geneva Convention), which held to the belief that FMJ ammo reduces suffering in war. It's a gentleman's agreement from an earlier age, and we never even signed it! We do, by our own agreement, follow it.
That's the "official" or "legal" reason. The real world practical reason is equally simple, it is because nothing else is as cost effective in accomplishing the mission. FMJ ammo is the most "durable" kind, and the most reliable feeding in automatic weapons. And, it costs the least. If there was anything else that out did FMJ in these categories, the world's militaries would use it. Count on that.
Remember the object of the military is to accomplish the mission. Their choices of what to use, and how to use it are NOT the same as the best choices for the survival and protection of the individual.
We want a round with good stopping potential, when we defend ourselves. Military priorities are different. They lean heavily towards what will deliver victory, not as much individual survival. Survival is the job of the individual.
Self defense and combat have some things in common, but are not remotely the same thing.
