The Sterling conversion utilized a separate ejector which entailed drilling a hole in the side of the receiver for the ejector itself. It had a spring that was fixed by the original ejector screw. The short answer is it isn't a factory Sterling conversion. There were barrels produced in Belgiumicon I think that were available in Canadaicon as well as those made by Canadian Arsenals so it could have been assembled by anyone. Are there any markings on the barrel?