sig sauer mcx .177 cal co2 powered advanced air rifle with co2 90 gram (2 pack) and 500 lead pellets bundle (black, 1-4x24 scope) sig sauer sig sauer mcx .177 cal co2 powered advanced air rifle with co2 90 gram (2 pack) and 500 lead pellets bundle (fde, 1-4x24 scope). from tactical drills to target practice, the co2 powered sig mcx air rifle delivers 30 rounds of rapid-firing, simulated sig mcx performance and handling for more realistic, economical training and practice — any time, any place. chambered in .177 pellet, features include an 18" rifled steel barrel, synthetic handguard, picatinny rail, tactical front grip, flip-up front and rear sights and more.