September 23rd 2023Note the shiny scratches on the bullets made by the comparator tool which indicates a point on ogive near where rifling will engage. The bullets have been scratched by the comparator tool, which shows a point near the rifling where the ogive of the bullet will engage.
Bryan Litz, Berger Bullets
Part One of this series focused primarily on the importance COAL has in relation to SAAMI standards. This included magazine lengths and seating depths. Cartridge Base To Bullet Ogive Length is another measure of length that is important for precision. Figure 2. Chamber throat geometry showing bullet jump from rifling to lands or lands.
Look at Figure 2. Imagine the bullet was seated so that the base of the nose (ogive), when the bolt is closed, just touches the beginning of riflings. This configuration is called touching the lands or touching the grooves, and it is an important measurement for precision hand loading. The distance that a bullet travels out of the case to engage the riflings can be critical to precision. This is due to the complex dynamics within internal ballistics, which occur in a blink of an eye. To optimize the accuracy of his handloads in a systematic way, it is critical that the precision hand-loader knows how to change the bullet seating depth relative to the barrel rifling. It is important to know how to measure the Cartridge Base To Ogive dimension (CBTO). This is explained in THE FULL ARTICLE.Bryan Litz provides an extended discussion of how to measure CBTO with different tools and methods including the Hornady OAL Gauge. This discussion can be found in the full article on the Berger Bullets site. Click Here to Read the Full Article. Why Not Use CBTO As a SAAMI Standard?
You might ask “Why isn’t CBTO listed as a SAAMI standard alongside COAL?” It is not listed because of one main reason. It is due to the lack of uniformity of bullet nose shapes and measuring instruments used to determine CBTO.
When checking the performance of your COAL, there is another reason to know your CBTO. You can easily achieve a CBTO of less than +/.001 with good bullets, tooling and carefully prepared cases. Your COAL can differ by as much as 0.025%. Extreme spread (or even more with other brands). This is not necessarily a bad thing. It is better than the alternative. If your CBTO dimensions are varying but your COAL dimensions are tight (within +/.002?) It is likely that the bullet is seated inside the seater cone at the tip. This is a bad thing and should be avoided. It is normal that bullets can have the same nose shape but also have nose lengths varying by as much as.025″?. Summary of Cartridge Base to Ogive Discussion
Here are four key considerations for bullet seating depth in relation to CBTO. CBTO is an important measurement for handloaders to understand because it directly relates to precision potential. You can control it by setting bullet seating depth. 2. CBTO can be measured using a variety of tools and methods. Before you start, you should be aware of the pitfalls that can lead to inconsistent results. 3. A CBTO which produces the best accuracy in your rifle, may not produce the same precision in another rifle. Even if the rifle, bullets, comparator gauges and other components are identical. It is possible that the gauges may not be the same and measurements from one do not translate to another. 4. It is important to maintain a minimum variation in the CBTO dimension when creating quality handloads. This can be achieved by using high-quality bullets, proper tooling, and preparing the case mouths and necks to ensure consistent seating. We welcome tips from readers.Similar Posts:Tags: Base to Ogive, Berger Bullets, Bryan Litz, Bullet Seating. We welcome tips and suggestions from our readers.Similar posts:Tags: Base To Ogive, Berger Bullets Bryan Litz, Bullet Ogive Seating, CBTO
