Sorry, but $0.40 per round is not a good deal, not even close.
Several places online sell 223 for $0.30 per round in boxes of 20, like Palmetto State Armory. Cabelas routinely has it on sale for the same price. I would never pay more than that for plinking ammo, which is pretty much all that low end stuff is good for, unless for some reason I was desperate.
I would not run steel cased ammo through my AR15 if it was free.