Thank you for joining the forum, but please don't belittle people.
It's called an assault rifle because most rifles were bolt action before assault rifles were introduced. All they used to have in the lines of fully automatic weapons were huge machine guns and sub-machine guns. Assault rifles came into play to fill a long needed void. A hard hitting round that could be used like a sub-machine gun. An assault rifle was born. It utilizes a slightly smaller rifle round, but much bigger than the sub-machine gun's pistol round.