http://cartridgecollectors.org/headstampcodes.htm
According to this link, it is one of these :
Hirtenberger Patronen-, Zündhütchen-und Metallwarenfabrik A.-G., Hirtenberg, Niederdonau, Austria
Rheinische Metallwaren und Maschinenfabrik, Dusseldorf, Germany
Winchester Repeating Arms...