Armed and DangerousG 50

Armed and Dangerous G50:
Collect 20 Legendary Weapons

Legendary weapons can be acquired randomly when you are out on quests, found when a dweller is exploring the wastelands, crafted in you weapon workshop, or obtained from opening a lunchbox. It doesn’t matter if you have duplicates of the same weapon and once you have received your 20th legendary weapon, the achievement will unlock.