The Extended Medium Mag II is a weapon modification that moderately increases the amount of ammo your compatible weapons can hold. This allows you to fire more shots before needing to reload.
You can obtain this mod by scavenging in the world. It can also be crafted at a Gunsmith station using the 
Extended Medium Mag II Blueprint and various other materials. Additionally, the vendor Shani sells this mod for 100 coins, with a daily limit of two per Raider. If you no longer need it, this mod can be recycled into other resources.
