Unmissable Xbox Achievement
Story spoiler free
To unlock the relative Quest: Complete the Quests named, Sonic Emitter Upgrade, Project X-13; X-2: Strange Transmissions, and have a conversation with Dr. Klein about Dr. Mobius, at the Think Tank - Dr. Klein is one of those human-brain-driven robots. You will acquire two more special equipment items by completing two specific Quests out of those three.
Following the Quest relative - Old World Blues: Activate the relative Quest, and complete that Quest simply as always, by following its Quest's logs, and the use of navigational aids. Recently acquired special equipment items are not required to be carried on your character during the relative Quest. But using that special gun is advisable, due to efficiency - also you can reset its condition upon recalibration, therefore are no Caps to invest to be required.
Xbox Achievement unlock: Upon completion of part five of relative Quest's logs.