It’s the Serbu RN-50.
Caliber: .50 BMG, .50 DTC for restricted markets. Other cartridges possible with barrel change
Action: Modified break action with threaded breech
Weight: 17 pounds
Barrel: 29.5 inches, alloy steel with 1-in-15 button rifling
Chassis: Heat-treated steel and aluminum construction
Finish: Manganese phosphate and hard anodized
Status: In production. Shipments started 5/17/16.
More info at Serbu Firearms
Hat tip to TFB