With Weapons Mastery, you will be able to craft the best weapon and equip it with the best ammunition, allowing you to destroy your enemies. This is a modlet, so you need to install it on a separate folder. Then, place the unzipped folder containing the mod into that folder. You are done! Now, you can enjoy the game in a different way, as you will be able to craft different weapons and equip them with different ammunition. You will be able to craft a marksman rifle and the Deadeye Master Perk book.