 The belt is for headspace as the cases' shoulders have a narrow slope rather than an actual shoulder.More modern magnums continue this practice, but headspacing on the belt is not necessary with their more sharply angled shoulders.The cartridge was used by American shooter Ben Comfort to win the 1000-yard Wimbledon Cup Match at Camp Perry in 1935, and it was used again to win the international 1,000 yard competition in 1937.