I have a 375H&H that is built on a W-R 318 Accellerated Express single square bridge action that appears to be the same action as yours. I believe the front ring on your action is relieved the same as on mine. The front ring rather than have a notch in the top for the long bullet has the front ring milled away from the top right side down to the rail. The amount removed is about the same depth as the single groove usually is and makes sense to me to facilitate loading of long rounds. My bolt handle is a regular Mauser tear drop bolt handle with nice engraving on the handle and the knob.