Welcome to the forum and you done good, nice piece, and we've seen a few like that with the powder residue , and was different each time some dried bluing salts, some maybe a dried moly lube, was told even a reaction of the aluminum and the anodizing residue, as you show how much is in the grip frame area, nice grips ,it could have shipped with them, never know, then it would be a RSSMW, not sure how they added whichever X and W, at the same time to the RSSM ( magnum and /or 6 1/2 inch barrel ) and your number puts it in the first run, of 1962 so would be a convertible, picture shows the serial number is stamped on the front of the cylinder , ( last three digits) very nice example and when you get the RENE you'll find out other details like the "eagle " rollmarked" on the barrel or not, and their serial number ranges ,all good info,,,sadly the lack of any letters right now doesn't help...as for the cleaning you done very good, we simply used mineral spirits, and soaked over night with the grips removed, kerosene worked as well....yes those old model action screws like you show the hammer screw were very rough, NOT finished , ( the head IS ) I think mainly because they would have then become undersized, cause hammer wobble....the cast parts were too close to the finish sized my guess......who knows that was a LONG time ago, and they still did a very good job with the castings of all their parts, crude, but good, and now today some are using MIM parts, ala S&W..........modern technology. still gotta love them old models though, enjoy it, you got a keeper......

