I have to say this, and I expect to be flamed. I am an avid gun lover. Understand that the 1st bullet you fire is going to make YOU the hunted.
Drop that weight and stock up on 1st aid, an axe, and a damed good knife. Make a surgical/suture kit a part of your pack. Add a blanket, and a 2nd multi-tool, and a fire starter kit.
Add a good set of optics, a compass, a whistle, and the slickest 1st aid manual that you can carry comfortably.
If you ever find the need to carry 400 rounds of ammo around don't worry. You will be able to pick up a gun off of a guy already dead in the street. Ammo won't be hard to find either.