I've not done this but it would likely entail the cost of a rebarrel. Not the cheapest thing in the world.. The cases are fairly similar although the 338 is anearly 1/2 inch shorter. This means the 375 would be an easier rebarrel but the 338 could be made to work. I would bet it would come out cheaper to trade the 338 for a 416..I would give preference to the Rigby round. It produces roughly similar ballistics at lower pressures.. and the 338 is just too nice a weapon to alter..