Umarex Heckler & Koch MP5 K-PDW. 177 Caliber CO2 Air Rifle. The HK MP5K-PDW Air Rifle features serious velocity: 400 fps. The semi-automatic action runs from a high capacity 40-shot mag. The BB repeater even has a realistic recoil action. A foldable stock, forearm grip, and drop-out magazine make this one of the most exciting and fun to shoot BB air guns ever created. Ready to shoot out of the box! No hustle searching for compatible accessories! Powered by one 12g CO2 Capsule. 177 Cal Air Rifle Specifications. 177 (4.5 mm) Steel BB. Capacity: 40 rounds (BBs). Weight: 3.70 lbs. Overall length: 24.5 in. Barrel length: 6 in. Umarex H&K MP5 K-PDW. 177 Caliber Air Rifle. If the wrong contact details are provided any losses incurred as a result will be the buyers responsibility.