What makes an upper lighter

This is my first AR build and this upper is heavier than the other aero uppers I’ve held. Does the barrel or hand guard have the most weight to it? This is a 16in btw. I want to take the weight down but still have reliability.

This is my first AR build and this upper is heavier than the other aero uppers I’ve held. Does the barrel or hand guard have the most weight to it? This is a 16in btw. I want to take the weight down but still have reliability.