I built mine on a 98 action

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It's essentially the same case as the 375 H&H sans belt, a tad shorter and with a 45 degree shoulder. It also pre-dates the 375 by two years. Bertram makes brass, but it's soft crap, Hornbear makes excellent brass but it's hard to come by. You can also tak 375 brass, chuck it in a lathe, turn down the rim, cut a deeper extractor groove and turn off the belt. Then fl size and hopefully the neck sets back far enough, then trim to length.