I'd guess that the Western Auto 9/Sentinel might
be the Western Auto name for the High Standard Double Nine.
The Double Nine looks looks like a SAA, but, as the name implies, it's DA/SA, and has a 9-round swing-out cylinder.
OP, does your gun look like a cowboy gun?
CajunBass, I have one coming that looks just like yours, but it's a R-107.
Edit: Here's a link to a Double Nine on GB.