I have done 2 massive loot runs where i cleared out the containers completely and watched the loot respawn infront of my own eyes and still no 5.56 ammo. Is this because 5.56 is classed as military? Might need to update one or two of the warehouses to spawn military type ammo instead to balance it out. Here is an image of my latest run where i looted the place twice in a row. https://ibb.co/dj6CtFt
Note: a pack is 4x box, a case is 4 packs or 16 boxes here.
I didnt loot all of the .22 .223 .38 or .44 on my second time round because i dont use it much but its blatantly obvious there is no 5.56 spawning here at all.