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According to Donnelly
From 303 to 44-40 turn rim to .525" ,back chamfer and cut case to 1.35" .Taper expand case mouth to .430" dia,F/L size.Trim to lenght, I.D. neck ream & chamfer. F/L size .
Most anything can be done with time and patience which you must have alot of Are these calibers in short supply your way? I am not sure but I would think the .303 walls would need to be thinned when compared to the originals.