Upper receiver in 5.56 NATO. Title pulled from psa website where purchase was made, although they're out of stock now. Played with it a couple times and it's not my preference. Lightly used every 6 months or so and I've had it for a couple years. It's a pretty sweet upper that can come with a mid BCG and a standard charging handle for an extra fee. Very willing to trade for optic risers, maybe an optic, something of equal value of course. Let me know or cash is easily acceptable.