It's a Magpul UBR, one of the nicest stocks to put on a XCR. Just make sure you have a NEA adapter it just doesn't fit as nice with dlask unit.
What he said
Albertanbound,
Since this photo was taken I've also added the MDT enhanced recoil pad and changed the muzzle brake to a PWS FSC30 Brake/Flash suppressor. And yes you can mount a sling to it.