Try sticking a magnet to it. That will tell you real quick if it is stainless or not.
Called Ruger earlier today and spoke with a very nice lady in customer service. I told her I was looking for information on a handgun I acquired and gave her the serial number. She laughed and said that's it?! I said yes it's an old one. She said it's a Ruger Single Six made in 1953. I asked if she could give me any specifics on it and was told to send an inquiry form in and it would cost $10 for a certificate of authenticity. So +1 to Ruger for great customer service!
I am debating on whether or not to send in for the certificate...what are your thoughts?