Both Dakota and Ultra Mag are variants of the 404 Jeffery, however all three have different rim diameters, the Dakota at 0.545”, the Ultra at 0.534” and the Jeffery at 0.537”. The Dakota brass is designed with an exceedingly proprietary thought in mind, same with reamer use. Dakota rifles are very much like what Weatherby was, perhaps even more proprietary whereby nobody chambers Dakota chambers in rifles except Dakota.
