http://w6oef77m5dfeiz6hzlurwf75cwcjhpcxyt6ys3dpvybetvk3d3drdoad.onion/hk-mr556a1-nato
Like the HK416, the MR556A1 uses a proprietary HK Short Stroke gas piston system instead of the direct gas impingement system found on lesser AR-15 style rifles. This closed piston system does not allow the exhaust gasses to enter the receiver meaning the HK runs cooler, cleaner and more reliably.