The salt cured wood really generates rust that aggressively eats away the metal anywhere the two are in contact.
The salt is in the wood from the quick-curing process. Rocksalt shoveled onto the blanks as they are stacked for normal drying.
Salt drawing moisture as it normaly does, draws the water out from the wood it is in contact with.
Salt curing wood was not a new trick. It was an old trick in the wood curing business and had been used for a long time.
Other trades using wood had used it.
Other gun makers had used it before FN/Browning.
I've had FN/Liege SxS and French SxS shotguns from betw the Wars that were heavily rusted inside from salt wood.
Here's a 1930's Belgian example. This one has the active rust nearly all cleaned up,,a few spots still active. No work was done yet to remove the pitting.
You can see especially on the under side of the forend latch where the wood contact was and was-not. Rusted and no-rust..
Most of the heavy pitting was then cleaned up on the inletting edges of the metal to get back to smooth surfaces. Files the primary tools.
The gun gets restocked so any changes in dimensions don't matter.
The wood is scrap though it can be used as a pattern. It can be used to turn a new stock (pre-carve).
That's what was done here.
The rusting action of the salt wood usually effects the outside surfaces of the gun as well if the gun has been around and together for any length of time. The Brownings have been.
The rust will have crept onto the outer surfaces from the inletted faces and grown. Heavier in some areas than others usually. I all depends on how much salt is in the wood and what the grain is in any one area. A more porous grain area will atract and hold more moisture from the air creating more rust on the metal.
Butt plate screws and grip cap screw will usually snap right off when you try to unscrew them. They will have been nearly eaten up by the rust.
Sling swivel screw screws as well.
Bbl surfaces under the wood line and just at and above it can be heavily pitted as well just like the frame.
All kinds of treatments have been used to stop the rusting and save the wood. Most of the salt wood from Browning was their fanciest grain stuff.
You hate to see the stuff go to waste. But putting it back on the gun is just asking for the same problem all over again no matter how you treat or seal up the wood.
Even the best methods fail. The best they do is hold off the rust better for a longer period than the other methods. The rust always wins.
As I posted on a Gunboard thread re: a saltwood Browning,,
FN burned all the salt cured wood in their inventory for a reason once the problem was discovered.
Winchester and Ruger also had some salt cured wood in their stock wood supply at one time. Ruger #1's show up with the stuff.
Salt curing is a quick way to get extremely expensive and valuable wood to market very fast. A few months instead of years
It's quick money if they can slip it past the buyers.