The bolt carrier group is the heart of your rifle, so it's worth spending a little here. This one is mil-spec dimensioned for 5.56 and .223, and it's finished in nickel boron. That coating is slick enough that carbon wipes off with a rag instead of a scraper, and it cuts friction inside the receiver too. Many shooters run these with very little lube. If you've ever spent an evening scrubbing a BCG, you'll appreciate the difference.