Jacketed hollow points are what you use to shoot people or animals with.
Full metal jacket rounds are practice rounds: cheaper because they’re easier to make. Of course, when you’re shooting on the gov’t dime, you can practice with full defense loadings.
Our troops get the shaft and have to use FMJ because of the 1886 Hague Convention’s obscure wording designed to make sure no scary future exploding rounds would be developed. I don’t know why the higher ups don’t just announce that the FMJ standard is BS and switch us to JHPs.
Whoops, 1899.