Actually... "assault" has a completely different meaning than aesthetics.

There are "battle rifles" and included under this umbrella is the M1 Garand, which is a larger caliber. The US Military realized that they needed a weapon that only shot out to 100-400(ish) meters rather than 700-900 meters, which was needed for WW1 & WW2. The "assault rifle" came about and actually refers to the ammunition rather than the weapon. The "assault" caliber is meant to take a person out of the fight rather than kill them.