Part of me wants to tell you that a private sale/barter is your business and no one else's. But since you asked, it would be prudent to call the local cop shop and ask whether or not a private sale of that quantity is legal. It certainly would be fine in New York...here's to hoping Illinois hasn't overtaken NYS just yet in insanity.
I wouldn't worry about it, it's not like ammo is registered to your name. Ask for cash payment and make use of common sense, if the person looks suspicious you can just refuse to sell, if it's someone you know personally I don't see any problem.