This afternoon I was installing a spring kit on my new M&P 340. While removing one of the screws for the side plate, the screwdriver blade moved a little sideways and scraped a sliver of frame metal at the edge of the screw hole. Wouldn't you know it? It is the uppermost screw, the one not covered by the grip.
Anyhow, I tried using a Birchwood Casey paint stick without good results. As a last resort, I tried a blueing stick. I assumed it probably would not work, since blueing is for steel and does not work on aluminum. But to my surprise, the blueing (actually matte black) stick worked and delivered results as if it had been applied to steel. The mistake I made is not even visible now after touching up. What a pleasent surprise!

Not trying to lecture, but please remember to run a bunch of carry loads through that 340 to make sure the spring change did not make ignition iffy. BTW, I own two M&P 340s; it's a magnificent gun, isn't it? Miles ahead of it's Titanium-cylinder "brother," IMO. We chose well!

Kaaskop49
Shield #5103

Already done!
Thanks for the thought.

Thanks for the tip on the cold bluing! I wouldnt-a-thunk-it on the alloy. M&P340 owner here too. I left the springs in mine after clicking it a bunch of times but I did do a full stone-polishing job inside which made it feel like glass.

I would keep an eye on it. A lot of acids will "burn" non-ferrous metals and turn it black. This could get under the aluminum oxide layer and screw up your finish. Just keep an eye on it.