Rifle Cartridge Powder / Load Density:
There are many rifle cartridge powders to choose from for the avid reloader today each of which vary in their burn rate. With all the powders that are available how does anyone know which powder to select for their particular rifle cartridge reloading.
Load density is the determining factor in selecting powder for a particular rifle cartridge with 86% density just about ideal in most cases. Load density is the ratio between case capacity and actual powder charge. Most factory ammunition is loaded with a density of 80% - 90% of the cartridge case capacity.
1. You should never exceed 95% load density.
a. Primers need room to flame through the powder charge which gives uniform velocity and pressure.
b. Cases that are full or compressed charges of powder will accelerate barrel wear in the rifle barrels throat area.
2. You should never drop to far below 80% load density.
A known condition named detonation (excess pressure spike) can occur with cases that are not signifacantly filled with powder. Some years ago the U.S. Ordnance and DuPont ballistics laboratories were able to duplicate the strange phenomenon called detonation and they had determined that excess air space in the cartridge case to be the trigger for detonation.
How to figure load density.
Powder charge weight divided by case capacity equals load density.
Example: Powder charge 40 grains (divided by) Case capacity 50 grains = .8 or 80% load density.
Case capacity is the amount of volume inside a cartridge case that is available for the powder to fill.
How To Measure Case Capacity.
Measuring case capacity is actually quite simple. Once you have established your bullet seating depth in the bullet section of this guide.
1. Weigh one case with bullet seated to proper depth without powder or primer.
2. Now fill the case with water through the primer hole using a hyperdermic needle and weigh again.
3. Now subtract dry weight from the water weight and this will give you your case capacity.
470 grains = water weight with bullet.
- 420 grains = empty weight with bullet.
50 grain = case capacity.
Once you have your case capacity using your reloading manual select powders that fall into your load density range.
In the above example of a 50 grain capacity your range would be.
a. 50 grain capacity x 80% load density = 40 grains of powder.
b. 50 grain capacity x 90% load density = 45 grains of powder.