I have my grandpas Revonoc 12 ga single shot shotgun. Over the Revonoc it says HSB & Co.
Serial #: 55585

Can any of you shed any light on this gun?

Thanks
AXEL

I think I can help you here: Revonoc is Conover spelled backwards, and Revonoc was a brand associated with the Conover Hardware Co., which was purchased at some point by Hibbard, Spencer & Barlett of Chicago, who either initiated the Revonoc brand or continued to offer tools bearing this brand. As your gun is also marked with the logo of "HSB & Co" this seems to bear this out.
That's all I know, if it's even true, and as always I'm looking forward to hearing more from the truly omniscient with more knowledge.
Regards,