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Exploding or expanding small projectiles were prohibited in international war before the Geneva convention. I think hollow points are prohibited by the Hauge Convention. The reason for this is they were supposed to cause unnecessary suffering and damage, more than was required to incapacitate a soldier.
Interestingly they also are the best ammunition for limiting damage to civilian bystanders, which is why they are commonly used by police. They are less likely to ricochet or penetrate a wall and accidentally hurt someone behind it,
If this story is true it may be because the U. S. army is expecting to be fighting in urban areas where there are bystanders who might get hurt.0