It's a Hop Up Chamber with a sensor to detect whether there are any BBs left and if there are none, it'll send a signal to the smart control unit, which it's connected to, telling it to stop firing so you don't end up firing blanks! The Hop up unit is made from a Shock Resistant Reinforced Techno-polymer, which makes it optimized for high performance hop up rubbers. It's adjusted with clicks so you can alter the hop up with precision and ease.
The ASHU Hop Up unit is for all AR15/M16/M4 AEGs with ASCU. When it's connected to the ASCU, the ASHU detects whether the magazine is empty and if it is, it'll stop the AEG from dry-firing. Because firing blanks makes the AEG feel inadequate... But once you press the Bolt-Catch, it'll resume firing!