Going crazy need to be educated.

[Ramson222]

Educate me on the center of mass and the center of pressure for a boolit.
Were should they be located and what they mean in regards to accuracy?
Im a sponge:)

[44man]

educate me on the center of mass and the center of pressure for a boolit.
Were should they be located and what they mean in regards to accuracy?
Im a sponge:)
what?

[onesonek]

Center of Mass is highly dependent on nose shape, length, and weight. Where it should depends on the twist rate, and boolit/bullet design. At least that's my limited knowledge of it. Because of varying designs, is why you see twist rates typical of production guns, a tad bit on the fast side. One needs at least a gyro stability factor of at least 1, to stabilize a bullet. The most accepted of a GSF, is 1.5 in order to take in account of rotational degradation, at longer ranges. Again, that is what I believe is correct, but could be off on some technicalities.
As for the other part of the question,,,,got me?????

[David Bachelder]

I'm not going to be a great deal of help But I can help define the terms.

Center of mass (center of gravity) is where the bullet would balance (similar to a balance beam).

Center of pressure is the bullets aerodynamic balance, a point on the bullet where there is equal aerodynamic pressure at all points.

For a bullet to have a stable flight (proper balance) the center of pressure must be behind the center of mass. A stable bullet would be more inclined to follow a stable flight path, therefore being more accurate than a tumbler.

Here is the same principle defined as it applies to rockets: http://my.execpc.com/~culp/rockets/Barrowman.html

I'm sure bullets are calculated differently than rockets, but it does provide some definition.

[Char-Gar]

The center of mass would be the theorical place in the bullets where everything in front and behind that bullet would have equal weight.

Target shooters has long used 38 Special hollow base wadcutter, because the hollow base placed more of the weight forward in the bullet and like a shuttle cock would be more accurate. So, I don't think "center of mass" is much to be concerned with.

I have no idea what "center of pressure" is or means, having never heard that term before so I can offer no opinion on that matter.

[Iron Mike Golf]

CG is the point that projectile rotates about when a force is applied to the bullet.

CP can be thought of as the point where the sum of all aerodynamic forces (drag, crosswind, etc) are applied.

You can easily visualize this by hanging a pencil from a string so it's level. The string is at the CG. When you poke the pencil with your finger and make it rotate, your fingertip represents the CP. So you can see how the CP being behind the CG acts to bring the nose back to the direction of flight.

This helps change where the bullet's "pointed" at during the entire flight. The nose basically stays pointed along the flight path even after it arcs over at maximum ordinate. In a vacuum, a bullet would remain pointed in the direction the bore was pointed all along its trajectory (it wouldn't nose over).

[Ramson222]

If im understanding this right CP should be as near possible to the base of a bullet while CG should be close to the mid point along the length.

In simplest terms the distance between the center of pressure and the center of gravity acts like a lever to push the nose of the boolit back into alignment with the flight path.

[Iron Mike Golf]

I don't know where optimum is. I do know that the CP shifts, especially as velocity goes supersonic to transsonic to subsonic.

ETA: Yes, the more distance between CP and CG, the more torque moment aerodynamic force has. You might want to read through Chapter 4 here: http://www.exteriorballistics.com/ebexplained/index.cfm

[Ramson222]

so bullet A. is more accurate than bullet B becuase as bullet B passes from supersonic to subsonic it will begin to tumble. Bullet C will be the most accurate because its center of gravity is closer to the nose than the other.
While bullet A and B don't actualy match my design (bullet C ) they do come close to it.
The red x is the center of gravity, while the blue line is the center of pressure.

BULLET A
http://castboolits.gunloads.com/imagehosting/thum_241984fdaa94d12173.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=5614)

BULLET B
http://castboolits.gunloads.com/imagehosting/thum_241984fdaa98ff0600.jpg (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=5615)

BULLET C
http://castboolits.gunloads.com/imagehosting/thum_241984fd7019eee4b6.png (http://castboolits.gunloads.com/vbimghost.php?do=displayimg&imgid=5578)