August 31st, 2018

Cartridge Base to Ogive (CBTO) Length — Factors to Consider

chamber length loading berger bullets
Here are two different bullet types, 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 rifling.

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.

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.
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August 31st, 2018

Lyman Brass Smith Presses on Sale at Midsouth

Lyman Ideal c-frone reloading press sale discount Midsouth

Midsouth Shooters Supply is running a big sale right on Lyman’s impressive new Brass Smith line of reloading presses. There are three models, each offering great performance and value for its class. You can save quite a bit of cash with this Midsouth Lyman Press sale. If you haven’t tried orange yet, we think you’ll be impressed. The little C-Frame is a steal at $69.99.

Lyman Ideal c-frone reloading press sale discount Midsouth

Lyman’s New Victory Single Stage Press competes with the RCBS Rock Chucker Press. If you like to prime on a press, this Victory has a priming system that’s much easier to use than the Rock Chucker system. With beefy Cast-Iron construction, strength and leverage is on a par with the Rock Chucker.

Lyman Ideal c-frone reloading press sale discount Midsouth

With a cast-iron frame, the Ideal C-Frame (open-front) press is stiffer than other small presses in this class. It is an excellent choice as an affordable, secondary press for your loading room, or a press to use at the range.

Lyman Ideal c-frone reloading press sale discount Midsouth

The new All American 8-Station Turret press sets a new capacity standard in a turret press. You get EIGHT stations, compared to 7 for a Redding turret and 6 for an RCBS turret. Lyman has also included a rear support that increase rigidity, reducing turret vertical displacement during loading. That helps load consistency.

Lyman Ideal c-frone reloading press sale discount Midsouth

NOTE: Along with the three individual presses, Lyman offers complete reloading kits combining the presses with powder measures, scales, and reloading tools. These kits are also on sale now at Midsouth.

Check Out New Lyman Presses in UltimateReloader.com Video
In this video, our friend Gavin Gear of UltimateReloader.com reviews all three new Lyman Brass Smith presses. He gives a quick over-view of their notable features. Gavin has loaded ammo on all three presses, and has tips on set up and installation. Check it out:

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