It looks like i need to kill 1344 Enemies in order to Auraxium the CHAINGUN https://imgur.com/IFEQUdI https://imgur.com/a/Mnj44lG https://imgur.com/IFEQUdI
Last I heard, that's a UI numbers bug on that particular menu; using the tracker via the Directives screen will correctly show the actual number of kills that you still need to make.