I have examples in front of me that I know are mady by Norma, RWS and Federal Cartridge Co.
I also have some headstamped “WEATHERBY ### WBY MAG” Made by an unknown company. They have a very US made look to them. The headstamp letters are smaller and more weakly struck than the Norma or RWS rounds. The primers are nickel plated and very flat. The bullet also have a US made look to them, with fairy pointed ogives and knurled cannelures. The calibres are .270, .300 and .340.
Where was the Weatherby company based? So I can put in my records as "Made by ??? for Weatherby Inc., Based in ???.