The broken shotgun is on the first floor of the mansion, near the room where the serum is located. It appears to be the same model as the regular shotgun. It cannot be repaired.
Location: The broken shotgun is on the second floor of the main house. It’s in Grandma’s room, locked by a scorpion door, and requires the scorpion key from the processing area to open it.
Purpose. The broken shotgun can be exchanged for a hanging shotgun in the Est Lounge on the ground floor of Spencer Mansion to allow the player to obtain the weapon without activating the falling ceiling trap. When playing as Chris, using the broken shotgun is the only way to get past the trap.
To repair the broken shotgun, simply combine the repair kit with the weapon and it becomes the M21 shotgun – one of the most powerful weapons in the game. While the M21 carries less ammo than its alternative at all times, it deals an obscene amount of damage and drops most enemies at close range.
Next to the medical storage room is a small storage room where you can pick up a broken shotgun. Collect it and from there go to the opposite side of the manor to the drawing room. The shotgun is on a row of hooks on the far wall that, when removed, set off a trap in the room.
The 44 MAG or Magnum is by far the most powerful weapon in Resident Evil 7. Other handguns just can’t match the Magnum’s damage per shot or per clip.