How many MOA do I need to reach out to 1000 yards?

[grayfox]

tdbru,

Correct, Centre-of-Pressure - my bad.

My understanding is that there is a most efficient shape for supersonic, and subsonic flight, and they are different to each other. For supersonic flight it is the Sears-Haack, and for subsonic it is a Teardrop. If your bullet impacts the target fully supersonic then the bullet should be similar to a Sears-Haack, pointy front and bulk to the rear. For subsonic the bulk is the opposite, CoG more to the front, a stubbier bullet like the Lapua 200gn 30cal for subsonic loads with a lock base. Same with aircraft; jet fighters vs. passenger planes.

As the bullet slows down it wants to reverse, weight forward, and spin stops it from doing that. But as I understand it, too much spin and it resists pointing down to the target after reaching the top of the curve or apogee 2/3 distance downrange. It wants to keep pointing at the sky and so it presents a yaw to the target as it approaches. Again, bullets that are still fully supersonic, above 1,350fps when they impact the target are easier to keep stable.

For F-Class anyone shooting .223 in our State had groups starting to blow out at about 800-900yds, and by 1,000 it was like they were drunk. Against the 308 guys we were fine until 800-900, and even had an edge with less windage needed, but it turns to custard after 800. Not many bullets to choose from in the 80-90gn range 223, maybe three: Berger, Hornady, Sierra. I understand there are other bullets in other calibres that are fine transitioning from supersonic to subsonic, retaining their accuracy as they do. It would just be a matter of testing different bullets and loads and that would be interesting.

Klem,
not to hijack the thread, but this is good stuff. Can you add some more on your statement "too much spin" - ie, spin/twist rates like 1:7, 1"7.5, 1:8, etc... I know for most cartridges there are standard recommendations but it would be instructive to see how this factors in to the yaw effect you mention.
thanks.