I have a Ruger Security Six....6" barrel in .357 mag. I received this from my grandma after my grand dad died in 2012. It is in about 90-95% condition with minor holster wear and only came with an old leather holster. She said he purchased it new between 1984-1986 (she's 92 and can't remember the exact year) I just pulled it out to look at it...and I cannot find a serial number ANYWHERE on it. It's in damn near perfect shape with factory bluing and nothing to indicate anything was "removed". Any ideas? Is this normal?