Bring your BB plinking game up a level with the HK 416. 177 caliber BB Air Rifle. This Air Rifle is powered by easy-to-find 12 gram CO2 (CO2 NOT included) and has a drop-free magazine that holds 500 BBs in its main reservoir and 36 BBs in the feeding portion. Reloads are fast and CO2 changes are very easy with this system. The HK 416 BB Air Rifle is loaded with plenty of Picatinny Rails for the attachment of optics and accessories. The HK Heckler & Koch HK416. 177 Caliber CO2 BB Air Rifle is sure to give fans of target hours of backyard shooting fun for years to come. This is the perfect Air Rifle for you. Ready to shoot out of the box! No hustle searching for compatible accessories! Powered by two 12 gram CO2 Cartridges. Single Shot or Six Shot Burst Mode. 36 Shot Feed Magazine. Picatinny Rail for Optics. Umarex HK Heckler & Koch HK416. 177 Caliber CO2 BB Air Rifle Specifications. 177 (4.5 mm). Capacity: 36 rounds (BBs). Weight: 3.95 lb. Overall length: 31.5” (80 cm). Barrel length: 13.5” (29.21 cm).