I came across this article on Facebook. Thought you all might find it interesting. It does use AR's for testing. 10,000 rounds fired through 4 identical AR's to figure out what kind of wear and costs are inherent with each type of ammunition.
Note: I am not posting this for flaming trolling or any other sort of Internet shenanigans.
http://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/