AR15 is not an assault rifle, AR stands for Armilite, it's a long barrel semi automatic
Guns like this aren't for shooting rabbits. They're for shooting people or they are convenient for this purpose. That's why they were banned in NZ, a country with very high rates of gun ownership, after the Christchurch massacres (the terrorist who shot the worshippers at the mosque used an AR).
They are guns with magazines that fire high-calibre bullets without the need to reload. You just pull the trigger. No bolt action etc, just bang bang bang.
Speaking as someone whose fired one (on a shooting range) they're extremely dangerous weapons.