Lots of interesting variations on Sterlingworths. I owned a very late 16ga that was flat sided. Didn't have the raised panels (or bosses) on the receiver. However, it was engraved as if the panels were there. There was some speculation that the receiver may have been made for an SP (which I believe is the only flat sided Fox), then finished as a Sterlingworth as Savage was ending production of real Foxes.