I swear to christ, Promethean Knights are the worst things ever, and the fact that watchers can resurrect them, made things so much worse. But a lack of ammo really never ever happened to me throughout the campaign once, there are usually weapons hidden around areas that I only discovered on this playthough.
My only advice for Legendary Solo is to keep weapons that are powerful and keep as much distance between you and the enemy. On some CQC levels always keep either a shotgun/scattershot or Sword/Hammer as a secondary as it will turn knights or Elites into swiss cheese., and a weapon that is capable of headshots, (DMR,Carbine,Magnum etc,)
My most used Armor Abilities were either the Hologram or Jetpack. The Cloaking Device only really helped in mission two for me.
