Stainless pitting under the grip.

[posigian]

I have a S&W 640 stainless revolver that I have been carrying since 2001. After years of sweat it is starting to pit just under the grips on the left side of the firearm.

Can this be saved, stopped, or polished back to its original form? Or is all hope lost and it will only get worse?

 

[Dfariswheel]

It can be stopped, and it can be polished out.
Polishing the pits out is the best option.

You can send it back to S&W to have it done, you can send it to a top gun refinisher service like APW/Cogan or Ford's, or you can do it yourself.

The best options are S&W or one of the refinishers. They can do it fast with no mistakes.

If you attempt it yourself, use wet or dry abrasive cloth wrapped around a wood block to keep the frame surface perfectly flat and even with no dishing it out or rounding it off.
Polish with a back and forth motion and inspect the surface often to make sure you're not tilting the block and rounding the flats off.
Once the pits are gone, switch to finer grits of abrasive to restore the factory finish. Since the grip frame is covered you don't need to do much past polishing the pits out.

To prevent rust in the future, get Johnson's Paste Wax or the very high grade Renaissance Hard Carnuba Museum wax. NO CAR WAX.
Apply a medium thick coat to the frame where the grips cover it and let it dry 30 minutes. Don't wipe the wax off.
Reinstall the grips.
The wax will protect the metal from moisture and sweat that leaks under the grips.

If the grips are wood you can also apply a coat of wax on the inside of them too, but don't apply wax to rubber grips.

 

[James K]

It is well to remember that stainless steel is correctly described as "rust resistant", not "rust proof". It can and will rust when the conditions are wrong; it just takes longer.

Jim

 

[mete]

That's the same thing I found on my HK P7. Though that's not SS.
Moisture with sweat wicks under the grips .Remove both grips ,clean , polish and coat with Wax or I used RIG preservative grease. Clean the back side of the grips too.
If you're worried about wax /grips reacting test a bit first.

 

[4V50 Gary]

What James K says. Stainless is rust resistant, not rust proof. It must still be cleaned and oiled.

After cleaning the gun, you might want to appy RIG Gun Grease on the affected part. Rig will provide a barrier between the metal and the corrosive effect of sweat. It doesn't hurt to wipe down the gun occasionally with a rag treated with gun oil.