Fully upgrade a weaponFor this achievement, you must get a weapon to Mk X (Level 10). You will need 11 Basic, 6 Advanced, and 3 Superior components to do this. Basic and Advanced parts are dropped and found as pickups or in chests fairly plentifully, but the Superior components only show up very late in the game and are quite rare. Don't upgrade a bunch of weapons to Mk 9 and have to farm forever to finally get one to Mk 10, use your first three to get this achievement out of the way.
Note: Upgrades on weapons are permanent, even if you sell the weapon. If you buy or find another copy of that same weapon, it will be at the level you upgraded it to previously.