Back in the day, standard military bore was 0.303" / 7.62mm. Now it's 0.556mm (0.22"). Ever wonder why? Military doctrine shifted post-WWII. There's the obvious "We can make more of the smaller ammo from the same amount of metal", but that's not the reason.
Military doctrine now is "wound, not kill". A dead body is a dead body. A wounded soldier will lie there screaming in pain & upsetting his mates. Someone may become another casualty trying to rescue him. All casualties, if they can be recovered from a battlefield, require care, soaking up manpower & resource, draining the enemy's materiel. A corpse doesn't do that. So shoot them with smaller ammo.