i dont know the answer to your question, but i can tell you how its derived.. this tecknique im sure is not exact but the priciple will do.. take the case with primer and seat a bullet empty. weigh it in grains.. remove the bullet, fill it with distilled water, and seat the bullet and weigh it and the difference in grains is the case capacity for that case and load.. whether you knotch the bullet before and after in the second load with water i dont know.. i did it once and the excess watter did not stick around without a knotch .. in my case it was very interesting, the black powder weight in grains was the same as the water weight in grains.. when they say 45-70 im guessing that the 70 is water capacity weight.. dont know for sure... when your doing very precise balistic programs they will ask for the case capacity, and the water weight is what they are looking for.. dave
