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Andrew Chamberlain

Modifying Parent Cases to Achieve Desired Power Potential

power-potential-parent case
Three categories combine to describe what I call the cartridge’s power potential. Therefore, understanding which loads in a particular cartridge produce the maximum velocity, maximum energy and maximum power is the key to understanding Power Potential.

 The World's Greatest Reloading Book — Handloader's Digest
The World's Greatest Reloading Book — Handloader's Digest.

Understanding power potential is the fundamental first step to understanding and simplifying the world of cartridges. The next step is to understand how power potential is affected, as well as limited, when that same case (or parent case) is manipulated to propel projectiles that are either smaller in caliber and inherently lighter, or larger in caliber and inherently heavier.

A parent case is exactly what it sounds like; it is the original & unique case from which new cartridges are built. For example the .30-06 Springfield is one of the earliest mass-produced big game cartridges. The .30-06 Springfield is also the parent case for many popular hunting cartridges. A small sampling of these include the: .25-06 Remington, .270 Winchester, .280 Remington, .338-06, and .35 Whelen.

A given cartridge has a perceived range of capabilities (or perceived power potential). New cartridges can be built from the existing cartridge to accomplish a new set of capabilities. This is done by simply changing one or more of the case’s three main physical characteristics. These are: 1-the neck diameter, 2-the case length, and 3-the shoulder height & angle. A fourth could be body taper, but that is much less common than the first three.

Neck Diameter: Reducing the neck diameter allows the cartridge to fire a smaller caliber bullet. Enlarging the neck diameter allows it to fire a larger caliber bullet. Manipulating the neck diameter tends to either increase bullet velocity or increase overall power potential (*not both*).

Case Length: Lengthening a parent case increases its powder capacity and increases its overall power potential. Shortening a case provides a smaller powder charge. This reduces recoil and overall power potential. But this can also increase powder efficiency. Manipulating the length of the parent case usually occurs in the draw process (when mechanically forming the case from a piece of brass). New improved powders occasionally allow a new cartridge to use a smaller case capacity and maintain a similar power potential as an older established cartridge that has a noticeably larger case capacity.

Shoulder: Manipulating the shoulder height and its angle can change how the burning powder builds pressure in the cartridge. This manipulates how the bullet is propelled out the barrel. “Improved” shoulders can increase velocity, powder charge and overall power potential.

The power potential of a parent case is governed by the fact that it has a fixed maximum powder load. As discussed above, power potential can be utilized to maximize velocity by propelling a lighter projectile. Or this power potential can be utilized to maximize energy & momentum by propelling a heavier and/or larger caliber bullet.

Editor's Note: This article is an excerpt from Handloader's Digest 19th Edition.


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