This is true, S&B rounds when shot hit for 1inch groups at 100m or better, the Hornady shoots on the exact same vertical plane but 8.5 inches lower....the Winchester hits 2 inches lower than the hornady …..the PPU rounds well I have never hit the paper with PPU rounds out of any of my 8mm rifles (I have no idea where the PPU bullets land, fired 40 rounds never bought them again)
I've used S&B and PPU ammo in my K98, and here are my observations:
-PPU always shot way low. At 100 yards, I found I had to raise the rear sight to about the 400m setting to hit zero.
-However it is worth noting that PPU makes TWO distinct flavours of 8x57. One, "8mm Mauser" is the anemic crap that everyone seems to carry in Canada. They make another blend called "8x57 JS" and according to the specs on the PPU website, is hotter than the first type, however I've never seen any of it in Canada. I'm assuming that this loading is much closer to what the rifle was designed for.
-The S&B ammo (and I've tried their FMJ and SPCE) is probably as close to the original specs as you're going to get. What I've discovered as a result of using this ammo is that my rifle is most likely zeroed for 300m, because at 100m my shots go like 6+ inches higher than POA. I wasn't able to access a 300m range to confirm this. I didn't observe any difference in the performance of the FMJ and SPCE at 100m.
The reason for these anemic loadings is that at one point early in the 20th century, the specs for the 7.92mm bullet were changed. The diameter was enlarged to .323 from .318 (if my memory serves me right), so since then manufacturers are paranoid about someone putting a .323 projectile into an old (ww1 and earlier rifle) and having it blow up on them, so they make all their ammo wimpy just in case.
One other anecdote I'll add, is that reloaders seem to prefer PPU brass over S&B brass. I think it has something to do with the primer pockets being more difficult to work with on the S&B brass.