I do my capacity measurements with deoxygenated water, since it's been sitting in a water bottle in my loading room for quite a while. But I doubt it makes as much difference as temperature, though most of us probably do it with water from 60-80 F.
The reason I do mine with a bullet seated, instead of full to the brim, is that's the "functional" case capacity. As an example, the most common .300 magnums have necks varying from .21 to .37 inch long, which alone will vary capacity approximately 3 grains.
But ALL those necks are filled with the shank of any bullet from 150 grains up. What matters more (though not as much as people think) is how much space the rear of the bullet takes up below the neck--given the maximum SAAMI length, though obviously a longer than standard magazine and throat length change things.
But all of that is MUCH more accurate than filling the case to the mouth, regardless of what kind of water is used. And it's yet another reason QuickLoad is only a very approximation of reality, no matter how many handloaders believe it's the word of some ballistic god.
