This unnamed Duke Arms Company special ops carbine is due to appear in Grand Theft Auto VI, seen wielded by Raul Bautista as he holds off VCPD officers in a video posted on the game's promotional website. Its design closely mirrors the standard Duke carbine but trades in a shorter barrel and a different stock, and it appears to take inspiration from the real-world M4A1 Block II rifle. No further specifications have been confirmed.
Weapon data via GTA Wiki (Fandom), CC BY-SA 3.0.