.223 twist needed for 75gr projectiles

[helotaxi]

Sectional density is the ratio of bullet weight to frontal area. It's really that simple. The shape of the bullet doesn't affect the SD at all. Doesn't matter if the bullet is a flat-pointed, flat-based dangerous game solid or a super long VLD, if two bullets are the same weight and same diameter, they have the same SD.

[M.O.A.]

But it doesn't effect it near as much so you would be closer by not measuring it

[helotaxi]

By that measure, you shouldn't include the jacket forward of the core on an OTM bullet either because the gilding metal is of lower density than the rest of the bullet and the air is of lower density still. Doesn't work that way there either. Density isn't the only consideration. The forward point of the bullet is important because of aerodynamic upset forces. Material doesn't matter.