Your post doesn't add up my friend. If your 338 has less brass in hdy than the others, than the volume should be more... The actual weight also does not directly correlate with the strength of the brass. That has more to do with the alloy and the annealing. I get that hdy did have a bad run of 338 Lapua brass early on, but from what I've heard things have changed.
Here's the measured Weight Data Grains:
Lapua Dry Filled with H2O
336.5 451.4 114.9
329.5 446.7 117.2
330.2 446.35 116.15
Avg. Case vol. water weight Lapua 116.1
Hornady
319.3 426.8 107.5
318.8 426.4 107.6
Avg. Case Vol. Water weight Hornady 107.5
Do your own comparisons. This was on once fired brass. Clearly the Hornady Brass weighs less Dry and has less volume of H2O
when filled. Could be its just shorter in the neck or case, or maybe it doesn't have the same alloy, weighs less and is less volume.
Yep, try this on your own too.