Hornady: "The list of cartridges and bullets is limited with this highly specialized powder, but where it works, it really works!>>> End of text."
* Generally speaking, what Horndy means is their powder is limited by cartridge and bullet weight, not so much bullet type or brand. "Conventional web/magazine wisdom" aside, no commercial bullets are meaningfully harder than others, it simply wouldn't be wise for bullet makers to market any bullets that would materially increase pressures and those people are not fools.
* Rifle and small, high intensity pistol cartridges respond to seating in a totally reversed manner. For rifle cartridges, seating deeper (within reason) actually reduces chamber pressure while seating out, closer to the lands, increases it. Letting a rifle bullet have a 'running start' at the lands allows it to keep moving from its own inertia while a rifle bullet starting at the lands demands a significantly higher pressure to force it into the bore.
* Military tests in the 1930s proved that by using standard military charges (and steel jacket bullets) in the .30-06; they found the highest pressures when seated well out, at the greatest possible internal volume. Seating the same bullets deeper reduced the peak pressure (and speed) until the bullet was fully 1/4" deeper before the decrease in internal volume finally started to produce a slight pressure reversal. Hornady's in-house experiments confirmed that effect with their own copper jacket rifle bullets in the 70s; it's well described and illustrated in their 3rd Edition loading manual (pg. 18).
* Only ammo makers need be concerned with how a case headspaces, rimmed, rimless, bottle neck, or how it's measured. What a reloader needs to do is size his bottle neck cases so the shoulder controls the headspace. That way it really won't much matter what the actual chamber headspace may be.