For this achievement, you'll need to pick up all weapons, with all possible attachments for each weapon. It is recommended that you try to pick up as many weapons (you can drop them immediately) during your first playthrough. Make sure you get to the next checkpoint if you plan to quit. Once you pick up all possible weapons with all possible attachments, you will unlock the achievement. Also, remember that you can use your visor :dup: to scan enemies and see the weapons that they are holding. You can view the video below for additional information.
The most difficulty, and most notable, attachments can be found below:
Bayonet: Safeties Off - At the very beginning of the level, there will be a large amount of enemies. One of them with carry the Marshall with bayonet, make sure to kill and check all the enemies once you kill them.
FY7 1M: Only Human - At the dead end, where you do the secondary objective where you rescue your teammates from the mines.
Extended Clip for Jackal: Red Star Rising - Can be found on enemies inside the base near the end of the level.