so does this mean that if for some really strange reason that I'm driving through Illinois as a non-resident and not having a foid card that I can't buy any ammo at all?
That is exactly what it means. I ran into this in Massachusetts.
Couldn't buy ammo reloading supplies or even dies. The clerk had to check with the Manager at Bass Pro before they would sell me a reloading manual. Hand to God it's the truth. I'm staying in Ohio...