They are hollow points essentially.
A hollow point is designed to expand on impact to slow down the trajectory of the bullet. In doing so, they travel through intended objects less often than other ammunition. Making them safer in self defense situations. And that is the reason people who intend to use firearms carry hollow point bullets. Not to cause more bodily harm. (the fact that they do is a byproduct of the attempt to make them safer)
As I mentioned, it is a probably a petty criticism, but I get irritated when people take this kind of view to emphasize the intention to kill or to hurt someone. i.e. the writer creates the view that Armstrong and Strickland purchased the bullets because of their ability to cause additional body harm. If you buy a firearm and intend to use it, then you intend to kill. I doubt that they chose those bullets because they cause more damage. People choose hollow points because they are safer to use.
