I had heard of this when I bought a stainless Ruger Old Army years ago - the big black powder revolver they made for many years. Black powder residue being particularly nasty if you don't get it ALL off, and hot soapy water being one of the recommended solvents, I removed the grips and took out the inner mechanical parts, then put the frame and cylinder in the dishwasher. Ran the full cycle, and the stainless parts came out pristine. But the black carbon steel front sight was covered in a thin layer of rust.

Probably shouldn't have let it go through the dry cycle. But it took so much trouble to get the rust off that front sight that I never tried the dishwasher again.