5.7 X 28 AR-15 Upper
Saw one of these installed on an AR-15 lower at a pawnshop in Fayetteville yesterday. Interesting novelty and at $859 cheaper than a FN PS-90 but I think I will stay with the 5.56, cheaper to shoot and easier to find ammo for.
Interesting but I would not like losing that much of the top rail.
Wow I didn't even know they made those. Cool.
One we installed for a customer was of pretty poor quality. Took a couple of days to get it to run at all.