When does the projectile sit properly on the powder charge?

The projectile sits properly on the powder charge when the mark lines up with the top of the muzzle. This positioning is crucial for ensuring proper alignment and stability during the ignition and propagation of the shot. When the mark is at the top of the muzzle, it indicates that the projectile is seated correctly, allowing for optimal performance of the firearm. This alignment helps in achieving consistent accuracy and prevents issues such as misfires or blooper shots that can occur if the projectile is improperly seated. Other options do not provide the correct indication of proper seating, as they may either lack sufficient seating depth or compromise the firearm’s functionality during use.