I have a ton of IVI 15 and IVI 18. I sold a bunch of LC 07 because I'm using the IVI exclusively. Never had to use a small-base die, though. Just the headspace/shoulder pushback being inconsistent.
The experts keep saying that case capacity is lower on military brass but I measured 30.4 gr H2O on the IVI 15 brass, pretty much the same as commerical R-P that I checked.
I noticed when sizing the once fired IVI that some cases were acceptable after being sized with a regular die, and some would not chamber.
I assume it depends upon what the chamber dimensions were in the rifle that fired the brass.
For the purpose of consistency, I sized the once fired brass twice, once with the regular sizing die and then again with the small base sizing die.
It was just too difficult to go straight to the small base sizing die as I got cases stuck in the die trying.
I just found my life was better by sizing the brass twice. This way yes the brass was on the small side, but once fired, they would then fit my chamber and volumetric differences would stabilize.
So, I have two loads, one for the first firing and one for the fire formed cases.
After they have been fired once, I revert to the standard minimal shoulder bump routine.
H2O capacity is a direct reflection of case weight with a once fired case, and not a meaningful means of sorting brass. The error in water variation from case to case is greater than the brass weight variation you are trying to measure.
All water does is give you a ball park sense of case volume, not an accurate measurement.