I've read up on Duracoat and Ceracote, but I'm not sure either would really stick on the stainless steel of a Smith 640. Anyone know of a good strong finish that'll stick on a this little J-Frame?

I'd like it to have nearly the same finish as a factory 442, but I'm not sure such a finish exists that simply won't wear off in a few months...

ION Bond is what the factory uses on the stainless cylinders of the M&P J-frames, Night Guards, etc.

Actually any of the DLC finishes will work just fine on the stainless 640.

Ferritic nitrocarburizing (Nitride QPQ) will turn stainless metal into a shade of matte black.

Before:


After:

How bad do the turn marks on the cylinder show up? Curious how many rounds you have thru yours there, after it was applied....

It had a line before I sent it in and came back with one. The treatment does not add a layer to cover anything up, it changes the properties of the metal on the edge to add hardness, reduce friction and increase resistance to corrosion.

After about ~60 rounds and 200 dry fires, there is a faint line (still a little wet from CLP):



You can see the line better with a flash, because of the way it reflects light:

Thanks for posting the pictures, I appreciate it!