SIG Sauer has been very busy recently. A new SMG prototype, a .308 piston AR10 already on sale to civilians, the ACP (a tactical pistol or optional SBR housing for pistols), starting work on the P227, the P938, a direct gas impingement AR15, and now a PDW in .300 Blackout. SIG announced it was manufacturing rifles in .300 BLK at SHOT last January, at AUSA 2012 they announced this SBR version with a PDR style collapsing stock.
Note this SIG516 is missing the single-point sling connectors on the lower housing, which have been relocated to the receiver extension, which is not covered when the stock is collapsed. I like that they were moved instead of just removed.
From The Firearm Blog.