Tuned Up Achievement
Customize all the internal parts of one weapon
Super easy. You will need 2 attachment credits. Just customize the Trigger & the Gas System for any gun. If any new attachment effects the guns stats take it off after the achievement unlocks. If you want this really quick, buy a Trigger for your Pistol and it will unlock.
Note: Unlocks after you have saved all the new upgrades. You unlock 1 attachment credits every time you level for Bodark & Ghost.