What is the difference between seating depth and shank seating depth?

Seating Depth denotes the distance from the base of the bullet to the mouth of the cartridge case. This measurement determines the extent to which the bullet is seated within the case and directly affects the Cartridge Overall Length (COAL) . Modifying the seating depth alters the internal volume of the case, which subsequently influences chamber pressure and bullet jump—the distance the bullet travels before engaging the rifling. Precise regulation of seating depth is critical for achieving consistent velocities and optimal accuracy. 

Shank Seating Depth pertains to the portion of the bullet's shank—the cylindrical section of full diameter—that is seated within the case neck. This measurement is especially important for ensuring proper neck tension and alignment. Adequate engagement of the shank within the neck assists in maintaining bullet concentricity and can affect the bullet’s release during firing. This parameter is utilized to calculate usable case capacity and to predict ballistic performance.