Today is the 30th anniversary of one of the most pivotal gunfights in US history, this event changed people's ideas on guns, ammo, tactics, big time.
One of the things coming from this fight was a scientific approach to wound ballistics, a subject that had been fraught with mythology, derp (still is sadly...) and a total lack of science. The ammo we have available nowadays came from the efforts to fix what was wrong with the ammo we had back then, how it was made, and how it was tested.
I think it also started to give cops the idea that a .223/5.56 carbine was a very good thing to have in a close range fight.