Had a guy I was talking to while enjoying my adult beverages yesterday evening assure me of the following:
He and his buddies buy "Tier 3 Tula 5.56" all the time because they can get it cheaper than "Tier 1" or "Tier 2" Tula. But the coating is corrosive, so you have to wipe down the rounds before you use them, or they'll corrode your barrel and trigger parts. However, once you wipe them down, they're fine, and well worth the hassle because it's only $0.02 a round. He said the coating was the same stuff you get old milsurp rifles coated in (aka Cosmoline).
He's also got several local stores where he gets "Tier 1" Tula for $2.50 per 20rd box...
And I missed out big when a local Bass Pro Shop opened up a few months ago. He and his buddy bought 15,000 rounds 22LR for $150, but it (the $10/1000 price) was an opening-day only special, so I missed out.
A local gunshop is cheating their customers, because they repackage "Tier 3" Tula into "Tier 1" boxes - but it's a conspiracy so that people will ruin their rifles shooting "Tier 3" without wiping it down, and have to buy new parts or new rifles from the same local gunshop.