I had heard that too, but I just finished analyzing some 30-06 cases that I fired in my rifle with strange results. I have federal cases and lapua case. The federal cases weighed on average 201.51gr + - .53gr and the Lapua cases weighted 197.5gr + - .31gr. The case volume H2O weight was 69.81gr + - .07gr for the federal and 70.49gr + - .21gr for the Lapua.
So the Lapua cases weighed less than the federal and had more case volume. They were fired from the same rifle, weighed on the same scale and I was careful to be consistent with the meniscus level of the water. The statistics were taken with and N of 10 cases. I was a little surprised to find that the federal case volume was extremely consistent while the lapua had three times the standard deviation. If I judged the lapua cases by weight then I would think they were more consistent, but the volume is the critical factor for the internal ballistics. strange results, huh?