Caliber: 5.56 NATO. Barrels: 13.7" and 16". Sons of Liberty Gun Works 4150CoMOV 1:7" MPI HPT. 1:7" twist, 1/2-28 threaded muzzle. .750" gas block journal with appropriately sized gas port. Other SOL lines include the EX03 Series, M4-89 Series, and M4-L89 Series. The MK-10 series of large-frame AR-pattern rifles was introduced in 2024.