From the Handloaders Manual of cartridge conversions.pg.482
Make from: Factory or 300 H&H magnum.Do not anneal cases.
Run into a 7x61 form die.Trim to 2.4".Chamfer.Full lenght resize.Fireform in chamber.They have had good luck making from 300 Winnie mag cases.Run into a 7mm/338 form die,cut to 2.4" and F/L resize with expander removed.Final trim,chamfer,resize with expander in placee,then fire form in chamber.
Mac