Hey Sean,There was a large batch of these rifles with blued bolts that turned up on Gunbroker from a seller in Michigan and they all came in a lot that they bought from Finland. Some were not even SA marked, but came with slings and dog collars. Some of the slings had SA marks on them.
Maybe it was a short term Finnish experiment in corrosion protection on bolts finished in the white. Not everything makes it into the books. Just like USMC M1903 characteristics. Brophy's book only mentions Marine sights. There are well over twenty Marine characteristics. Sure the same applies to every milsurp rifle that we collect. See it here almost everyday. Thanks for your info. I'd like to see a photo of one of those "Blackened" Finn bolts.