Sterling Steel appears to be an early fluid steel
Forest & Stream 1891
https://books.google.com/books?id=9kchAQAAMAAJ&pg=PR8&lpg

It was mentioned briefly in Greener's 1891 Modern Shotguns, but not in the 1907 edition of The Gun.

It was not listed in the 1891 Proof House Report
http://books.google.com/books?id=inQCAAAAYAAJ&pg=PA9