October 26th, 2014

Berger Article on COAL and Cartridge Base-to-Ogive PART 2

Berger Bullets COAL length cartridgeEffects Of Cartridge Over All Length (COAL) And Cartridge Base To Ogive (CBTO) – Part 2
by Bryan Litz for Berger Bullets.
Part One of this series focused on the importance of COAL in terms of SAAMI standards, magazine lengths, seating depths, and pressure levels. Another measure of length for loaded ammunition is highly important to precision, namely Cartridge Base to Bullet Ogive Length (CBTO).

Figure 2. Chamber throat geometry showing the bullet jump to the rifling or lands.
chamber length loading berger bullets

Look at Figure 2. Suppose the bullet was seated out of the case to the point where the base of the bullet’s nose (ogive) just contacted the beginning of the riflings (the lands) when the bolt was closed. This bullet seating configuration is referred to as touching the lands, or touching the riflings and is a very important measurement to understand for precision hand-loading. Due to the complex dynamics of internal ballistics which happen in the blink of an eye, the distance a bullet moves out of the case before it engages the riflings is highly critical to precision potential. Therefore, in order to systematically optimize the precision of his handloads, it’s critically important that the precision hand-loader understands how to alter bullet seating depth in relation to the barrel rifling. Part of the required knowledge is understanding how to accurately and repeatably measure the Cartridge Base To Ogive (CBTO) dimension. This is explained in the FULL ARTICLE.

Bryan Litz offers an extended discussion on how to measure CBTO using different tools and methods, including the Hornady OAL gauge. You can read this discussion in the full article found on the Berger Bullets website. CLICK HERE to Read Full Article.

Why Not Use CBTO as a SAAMI Standard?
If CBTO is so important to rifle accuracy, you might ask, “Why is it not listed as the SAAMI spec standard in addition to COAL?” There is one primary reason why it is not listed in the standard. This is the lack of uniformity in bullet nose shapes and measuring devices used to determine CBTO.

Figure 4. Two different bullet shapes, seated to the same CBTO length, but different COAL. Note the shiny scratches on the bullets made by the comparator tool which indicates a point on the bullet ogive near where the ogive will engage the riflings.

chamber length loading berger bullets

Benefits of Having a Uniform CBTO
There is another aspect to knowing your CBTO when checking your COAL as it pertains to performance. With good bullets, tooling, and carefully-prepared cases you can easily achieve a CBTO that varies less than +/- .001″ but your COAL can vary as much as .025″ extreme spread (or more with other brands). This is not necessarily bad and it is much better than the other way around. If you have a CBTO dimension that varies but your COAL dimension is tight (within +/- .002″) then it is most likely that your bullet is bottoming out inside the seater cone on the bullet tip. This is very bad and is to be avoided. It is normal for bullets to have precisely the same nose shape and it is also normal for these same bullets to have nose lengths that can vary as much as .025″.

Summary of Cartridge Base To Ogive (CBTO) Discussion
Here are four important considerations regarding bullet seating depth as it relates to CBTO:

1. CBTO is a critical measurement to understand for handloaders because it’s directly related to precision potential, and you control it by simply setting bullet seating depth.

2. Tools and methods for measuring CBTO vary. Most of the measurement techniques have pitfalls (which may give rise to inconsistent results) that you should understand before starting out.

3. A CBTO that produces the best precision in your rifle may not produce the best precision in someone else’s rifle. Even if you have the same rifle, same bullets, same model of comparator gauges, etc. It’s possible that the gauges are not actually the same, and measurements from one don’t translate to the same dimension for another.

4. Once you find the CBTO that produces the best precision in your rifle, it’s important to allow minimal variation in that dimension when producing quality handloads. This is achieved by using quality bullets, tooling, and properly preparing case mouths and necks for consistent seating.

CLICK HERE to Read Full Article with More Info
Article sourced by EdLongrange. We welcome tips from readers.
Permalink Bullets, Brass, Ammo, Reloading 6 Comments »
October 26th, 2014

Walt Berger Earns 20th Hall of Fame Point at NBRSA Nationals

Here’s a feel-good story, particularly for those of us getting up in years. Walt Berger recently proved you are as young as you feel — and you can enjoy shooting success at any age. Walt Berger, well into his 80s, won a big benchrest victory last month, taking the Sporter Class 100-yard Aggregate at the 2014 NBRSA Score Nationals. In so doing, Walt earned his 20th Hall of Fame Point. That’s a great accomplishment for the Elder Statesman of Benchrest. Congrats to Walt! And, yes, of course, Walt was shooting a projectile made by Berger Bullets — the 6mm 65gr BT Target bullet.

Walt Berger NBRSA Hall of Fame

About Walt Berger
Walt Berger started making rifle bullets in 1955 because he believed he could make better bullets than those that were available at the time. He regularly participated in benchrest shooting competitions (and still does today), which requires the highest levels of precision in all components. In 1987, Walt grew his bullet making operation beyond a part time hobby after encouragement from his second wife Eunice (Walt lost his first wife Mary to cancer). Together, they grew the business into a large-scale precision rifle bullet-making operation.

Walt was born at the end of the Golden Twenties and the beginning of the Great Depression. His story is about overcoming great odds and seeing things through to success when almost everyone around him was convinced he would fail.

Walt Berger with two younger generation Berger Bullets employees at the 2014 NRA Annual Meeting.
Walt Berger NBRSA Hall of Fame

Permalink Bullets, Brass, Ammo, News 4 Comments »
October 26th, 2014

Save on AR-15 Parts during Six-Week Brownells Sales Event

Brownells is offering more than month of deals on AR-15 hardware. Brownells’s “Back In Black Rifle Event” features six weeks of special, discount pricing on AR-15 upper receiver parts kits and accessories. The event culminates with blowout specials on the official Black Rifle Friday Weekend (from Friday, November 28 through Cyber Monday, December 1st).

Each Monday, leading up to Black Rifle Friday, Brownells will unveil a new package that includes all the required parts (except for lower receiver) to build a different version of the AR-15. Every package will give customers significant savings compared to buying all the parts separately(and eliminate the chance of overlooking important items).

Brownells Sale AR-15 Black Friday

Customers can see a new AR-15 package every Monday, from now until November 24, by visiting the Black Rifle Event Page at Brownells.com.

In addition to the main sale on AR-15 components and tools, some weeks will feature specials on 1911 magazines and parts, as well as accessories for Remington 870 shotguns.

Permalink Gunsmithing, Hot Deals No Comments »