CBTO, in the context of cartridge preparation, denotes Cartridge Base To Ogive. It is a measurement used to determine the distance from the base of a cartridge to a specific point on the ogive of the bullet. This measurement provides a more consistent and reliable method of setting bullet seating depth compared to measuring overall cartridge length (OAL). For example, a reloader might aim for a consistent CBTO measurement when loading ammunition for a specific rifle, ensuring that the bullet engages the rifling in a predictable manner.
The significance of utilizing the CBTO measurement lies in its ability to mitigate variations caused by bullet tip inconsistencies. Bullet tips can vary in shape and length, leading to inconsistencies in OAL measurements, which in turn affect internal ballistic performance. By focusing on the ogive, which engages the rifling, reloaders achieve more consistent bullet seating depth and improved accuracy. Historically, reloaders relied on OAL; however, the shift towards CBTO reflects a desire for increased precision, particularly in competitive shooting disciplines. This pursuit of precision enhances accuracy and minimizes pressure variations.
