In Valor Mortis, upgrading your firearms takes Firearm Parts, and they come in four tiers: Standard, Superior, Exquisite and Masterwork. The first three take a firearm up to its base, upper and advanced levels, but to push a firearm to its highest level you need the rarest of them all: Masterwork Firearm Parts.
There are only 3 Masterwork Firearm Parts in the whole game, but that is exactly enough to fully upgrade all 3 firearms, so you never have to choose which one gets maxed out. Upgrading a single firearm to its maximum level also unlocks the “Gun of Glory” Trophy/Achievement.
This guide lists the location of every Masterwork Firearm Parts, so you can grab each one as soon as you reach its area and take your firearms to full power at James's Iron Bench in the Abandoned Church.
Masterwork Firearm Parts 1
The second Masterwork Firearm Parts can be found in a chest near the "Sewers" Lantern in the City of Orphans region.
But first we will need to find the "Sewers Master Key", to do so start from the Sewers Lantern and advance on the main path until you reach the open room with the first Grappling Point, here go through the gate on the left (the one we needed the regular Sewers Key for during the main story).
In the next area go left until you reach the end of the tunnel, here go left again and just before the shortcut that takes you back to the Sewers Lantern you will see a pole you can jump across to on the left.
Use this pole to swing across to a platform on the other side where you will find the "Sewers Master Key".
Now that we have the key, the chest containing the Masterwork Firearm Part is very easy to find, swing back across the pole and open the shortcut on your left back to the Sewers Lantern.
We can now use the key to open the gate directly beside the Sewers Lantern, which is where you will find the chest.
Masterwork Firearm Parts 2
The first Masterwork Firearm Parts are the reward for completing the “The King of Smugglers” side quest, which starts near the "Ship Graveyard" Lantern in the Vale of Wrath region.
From the Ship Graveyard Lantern, turn around and swing back across the broken bridge, on you right you will see a poison mist path that you can only travel through if you have the Shield Transmutation (which you unlock during Chapter 8 of the Main Story).
This poison mist path will take you to the docks, here jump across to the main center platform and go down the small ramp on the right to reach under the pier.
In this lower area, go all the way to the left where you will find a note on the ground behind some boxes just to the left of a ladder. Read this note to start the Side Quest.
Later, in The Outskirts region, head to the "Harbour" Lantern and go to the right through another poison mist path by using the Shield Transmutation, in this are go onto the boat at the far right side where you will find an Elite Enemy inside the boat, this Elite will drop the "Harbour Residence Key".
Once you have the key, leave the boat and use it to enter the nearby house (the one being guarded by the tall Volunteer enemy).
Inside this house you will be able to read Crusty Benek's Journal. This completes the quest and rewards you with the Masterwork Firearm Parts and 5,000 Catalysts.
It is worth noting that you can do this Side Quest in any order, if you read the Journal in The Outskirts first, the Quest will complete when you then read the note in the Ship Graveyard.
Masterwork Firearm Parts 3
The final Masterwork Firearm Parts can be found in a chest in the University region.
Starting at the "Main Hall" Lantern, go up the stairs and go through the center main shortcut door.
In this first hallway go through the door on the left, when you reach the room with the stairs, go up the stairs and turn left just before reaching the balcony area with the tall Volunteer enemy.
When you reach the room with the thin planks you can walk across, go across the planks and turn left at the other side, here crawl through the hole to reach the room with the chandelier, to the right is a hallway covered in poison mist, use the Shield Transmutation to go through this poison mist, shortly after you will go down a lift to reach the lower area.
In the lower area , turn left when you can to reach the left side where you will find a tall Volunteer enemy shooting at you, go through the hallway behind this tall enemy to reach a big lecture room.
The chest containing the Masterwork Firearm Part is behind the ladder near the back of this lecture room.
