>>370804567
quality of a crate's loot depends on three things:
color of crate
your security level
the "level" of the zone it's in

So a white crate in Kolhoz or Castle on the max security level is going to have the best loot.

But there's a hand-placed stash for almost every gun, so read the notes you pickup and pay attention. Crate loot is a meme.