well, I bought the nightscope for the varmint rifle. How do I put this thing on? Anyone figured this out yet? Also, can you only have one modification on a weapon at one time, or can i put extended mags on it as well?
Open up your Pipboy Inventory and go to a given weapon... if you have mods for that weapon in your inventory, there should be a "Mod" button enabled & lit up, in the upper right hand corner. Click that and it'll open up a submenu allowing you to slap the mod onto the weapon.
Mods are weapon specific - the Ext. Mag mod is for one of the pistols.