I had/have the exact same problem with my 29-2. One small rust spot behind the smith and wesson on the barrel ( 6.5 "). About the size of a pin head maybe a tad larger, I cleaned it out swabbed it out with alcohol, I heated the barrel with a hair dryer, and used G96 liquid gun blue, then a second coat, it wasn't the saw blue but close, Then I took a clear nail polish and dabbed it, let it dry then again, let it dry, next day I used the roughest paper towel I could find and buffed it until I was able to notice it but not to bbad and a lot better than when I started, I screwed up in the first place and I'm not trying to put a fix on to fool anyone, but its been 6 months now and there is no open wound, and I don't want to lose the original saw blue.
Just my story for what its worth, and I know solvents will remove this fix and I'll have to do a makeover.