first, thank you for the link to the paper on the subject.
I neatly illustrates the problem as I see it: a lot of words and no factual data. Nobody doubts that boattails do reduce drag significantly in the transonic and subsonic regions. But the days of long range machine gun fire are long gone.
Nevertheless, 7.62 NATO and 5.56 NATO have boattail bullets. Practically every Match bullet (sole exception Lapua G490) has a boattail. So I would like to know (preferably in reliable numbers) what the real world advantage of these bullet shapes compared to flat base is at typical rifle distances, which are supersonic to the target. We simply do not have such data as far as I now. My provocative statement has been that Match bullets only have a boattail because it looks so much cooler than a flat base.
As I wrote, currently the only reliable source are G7 and G8 drag models, which are based on the same bullet projectile shape with/without boattail. But these were obtained with 76 mm projectiles (at Shoeburyness) and 40 mm projectiles (at Woolwich). We know from experiments that differences in drag of 10 percent between an artillery projectile and its scale model in 12.7 mm do occur. The difference between G7 and G8 is of the same order, so we cannot be sure that G7/G8 reflect the real difference for rifle projectiles. This is why I am trying erverything to lay my hand on any data that can shed light on this question.
A word regarding “at all speeds”: G7/G8 show clearly that above Mach 2.9 drag is identical up to about Mach 4, where the boattailed again has an extremely small advantage. But these are speeds well above rifle velocities.
This is one disadvantage of seeing ballistics from the BC viewpoint: subtleties of air drag are totally submerged in the fixation on BC.