01-07-2022, 10:19 PM
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.
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.