Just some information for anybody going for Lone Wolf Legend (solo Legendary playthrough) wondering if this is difficult to do solo, or hate doing multiple playthroughs of missions (like me) or messing with a second controller:
In my opinion yes, this is absolutely doable solo Legendary and does not hinder your ability to play the level that much. Playing on Legendary can be difficult but I don't think going for this achieve at the same time makes it any more so.
Be sure to scope out every area for ammo crates. There are PLENTY of Promethean weapons laying around and ammo caches, and some Covenant. They can be standalone or hung on walls.
It does not matter if the UNSC weapon is empty, so don't be afraid to use it in a tight spot. I finished the level with an empty AR and got the achievement.
The Light Rifle is a very powerful weapon and mainly what I used throughout the level.
I was really surprised to see such a high ratio (almost 5.0!) on an achievement that is not that difficult, go out there and get this!