This is a Sig Sauer MCX Semi-Automatic .177 CO2 Air Rifle.
This one has a 30 round belt-fed pellet magazine, which is powered by 90g CO2 cartridges. Velocity of up to 700 fps.
Features include an 18" rifled steel barrel, synthetic handguard, picatinny rail, tactical front grip, flip-up front and rear sights.
Also comes with a 1-4x20 CP Tactical scope, tactical bag, CO2 and pellets.