Effects Of Cartridge Over All Length (COAL) And Cartridge Base To Ogive (CBTO) – Part 1
Considerations for Magazine Feeding
When a hand loader is working to establish a seating depth to use with a particular bullet, he must decide if he needs the cartridges to feed thru a magazine or not. If the shooting application is hunting or tactical shooting, then the shooter probably needs the rounds to cycle thru the magazine so the rifle can be used as a repeater. However, in many slow fire target shooting applications, it's not necessary to magazine feed the cartridges.
Often times when a shooter doesn't need to feed rounds thru a magazine, the shooter can take advantage of substantial performance improvements by loading the bullets out long. This brings up an important reality of seating depth and COAL.
SAAMI COAL Limits Ballistic Performance
It is a fact that the ballistic performance of modern ammunition is directly limited by the SAAMI COAL standards that are currently in place and that rifle manufacturers build to. Even when a shooter understands the implications of cartridge case volume and has a chamber that allows them to load the rounds out long, the rifle itself (having been built to feed SAAMI length cartridges) won't allow the shooter to do so.
This fact is one reason for the popularity of custom rifle builders who understand the importance of feeding longer than SAAMI length rounds and building rifles with long enough actions and magazines to cycle the rounds. The first commercial rifle manufacturers who figure this out and start building rifles capable of feeding longer rounds will lead the way into modern times. There have been many improvements to several key components of modern rifle ammunition, specifically bullets and powder. It's unfortunate that many rifle makers continue to adhere to the antiquated SAAMI limitations that were put in place so long ago when components were so different, standards which limit the performance of modern potential.
Summary of COAL discussion
To recap the important considerations regarding bullet seating depth as it relates to COAL, we can say:
– Seating a long bullet to the restrictive SAAMI COAL can severely decrease the internal volume of the cartridge which will limit the max velocity the cartridge can achieve.
– If magazine feeding is not a requirement (or if you have a longer than standard magazine) you can load your bullets long, which increases the volume for powder and allows you to use more powder and achieve faster MV for the same pressure.
– If you load the bullet too long and it encounters the lands, this can elevate pressure due to the engraving force resisting the bullets' initial forward motion.
The second half of this article will discuss the differences between Cartridge Over All Length (COAL) and Cartridge Base To Ogive (CBTO), and why a working knowledge of both is beneficial to shooters and reloaders.
Bryan Litz majored in Aerospace Engineering at Penn State University and worked on air-to-air missile design for 6 years in the US Air Force before taking a job as Berger Bullets Chief Ballistician in November 2008. Bryan has been an avid long range shooter since the age of 15. In particular, Bryan enjoys NRA Long Range Prone Fullbore/Palma competition and is the current National Palma Champion. Bryan is also a husband and proud father of 3.
When a hand loader is working to establish a seating depth to use with a particular bullet, he must decide if he needs the cartridges to feed thru a magazine or not. If the shooting application is hunting or tactical shooting, then the shooter probably needs the rounds to cycle thru the magazine so the rifle can be used as a repeater. However, in many slow fire target shooting applications, it's not necessary to magazine feed the cartridges.
Often times when a shooter doesn't need to feed rounds thru a magazine, the shooter can take advantage of substantial performance improvements by loading the bullets out long. This brings up an important reality of seating depth and COAL.
SAAMI COAL Limits Ballistic Performance
It is a fact that the ballistic performance of modern ammunition is directly limited by the SAAMI COAL standards that are currently in place and that rifle manufacturers build to. Even when a shooter understands the implications of cartridge case volume and has a chamber that allows them to load the rounds out long, the rifle itself (having been built to feed SAAMI length cartridges) won't allow the shooter to do so.
This fact is one reason for the popularity of custom rifle builders who understand the importance of feeding longer than SAAMI length rounds and building rifles with long enough actions and magazines to cycle the rounds. The first commercial rifle manufacturers who figure this out and start building rifles capable of feeding longer rounds will lead the way into modern times. There have been many improvements to several key components of modern rifle ammunition, specifically bullets and powder. It's unfortunate that many rifle makers continue to adhere to the antiquated SAAMI limitations that were put in place so long ago when components were so different, standards which limit the performance of modern potential.
Summary of COAL discussion
To recap the important considerations regarding bullet seating depth as it relates to COAL, we can say:
– Seating a long bullet to the restrictive SAAMI COAL can severely decrease the internal volume of the cartridge which will limit the max velocity the cartridge can achieve.
– If magazine feeding is not a requirement (or if you have a longer than standard magazine) you can load your bullets long, which increases the volume for powder and allows you to use more powder and achieve faster MV for the same pressure.
– If you load the bullet too long and it encounters the lands, this can elevate pressure due to the engraving force resisting the bullets' initial forward motion.
The second half of this article will discuss the differences between Cartridge Over All Length (COAL) and Cartridge Base To Ogive (CBTO), and why a working knowledge of both is beneficial to shooters and reloaders.
Bryan Litz majored in Aerospace Engineering at Penn State University and worked on air-to-air missile design for 6 years in the US Air Force before taking a job as Berger Bullets Chief Ballistician in November 2008. Bryan has been an avid long range shooter since the age of 15. In particular, Bryan enjoys NRA Long Range Prone Fullbore/Palma competition and is the current National Palma Champion. Bryan is also a husband and proud father of 3.
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