Since we have a revolver confirmed for the game, and we are able to load spent cartridges, a neat little detail that would be nice is primer dimples on fired cartridges as seen in the photo.
It’s a nice piece of detail not seen in many games and would be helpful for revolvers, break action shotguns, and other firearms where the back cartridge can be seen. It also adds to the immersion of the game.
For reference, the left is unfired, and right is a spent casing