Weapon Master, 4th Variant (5e Feat)

You have extensive mastery with a variety of weapons, gaining the following benefits:

You gain proficiency with four weapons of your choice. Each one must be a simple or a martial weapon.
Choose three weapons you're already proficient with. The weapon die for those weapons are now one die size bigger. For example, a Dagger's weapon die would now be 1d6 instead of 1d4.