I have a new old stock sharon barrel and your breech looks just like mine. From the few others I've seen the stamping can be fairly shallow and fine. My crown is different from yours and the one pictured above, but that doesn't mean much, rifling looks the same.
On a side note i did once find a douglas barrel stamp under the barrel rib, just a suggestion if ypu can't find it with the chalk trick.
On a side note i did once find a douglas barrel stamp under the barrel rib, just a suggestion if ypu can't find it with the chalk trick.