https://www.washingtonpost.com/news/morning-mix/wp/2014/08/1...
Full metal jackets are required for war, while law enforcement use bullets for stopping power.
One way the U.S. could reduce gun deaths would be to require full metal jacket ammunition; It decreases the likelihood of death for any given hit; (though increases ricochets and likelihood of stray bullets)(also increases price of every bullet sold)
Law enforcement and other self-defense applications use hollow-point (HP) bullets to minimize penetration for the safety of innocent bystanders. The idea is that the bullet is designed to not fully penetrate the first material object it comes in contact with, though over-penetration can still happen. A full metal jacket (FMJ) bullet will frequently go through multiple walls and bodies until it depletes its energy, which is desirable in military applications; the design of military bullets enhances this.
The prohibition on HP bullets from the Hague Convention is a 19th century anachronism based on the capabilities of firearms from that period, modern rifle bullets have significantly different design requirements in any case. Modern high-velocity FMJ cartridges, such as the ubiquitous 5.56mm NATO, can undergo explosive fragmentation which causes much more damage than the low-velocity use cases for HP.
FMJ is typically cheaper and feeds more reliably than HP bullets, particularly in dirty firearms, which is a major consideration for the military since the advent of semi-automatic and automatic weapons a century ago.