As with all rimless cartridges (those without rims or belts used for headspacing) the .35 Remington headspaces on the shoulder. That's what stops the forward movement of the case in the chamber when fired. Since the shoulder of the .35 Remington is rather small, it is critical that you set up your sizing die so it does not "set back" the shoulder. All my resizing dies are set up to headspace on the shoulder of the case be it rimless, rimmed, or belted magnum type. Easy to do and case life will be greatly improved and it will help prevent the nasty situation of case head separations in your rifle's chamber. I also check each and every rifle case with a #6 crochet needle by running the point of crochet needle along the inside of my case from base to shoulder. The point of the crochet needle will "catch" on any groove inside the case, signalling an incipient case head separation will occur very soon. When my crochet needle catches on a groove inside the case, it's time to add that case to the scrap recycling can.