How to determine the bulk density (Pcd) for your powder lot in GRT

Author: Charlie

To use GRT to determine the Pcd value requires fooling GRT a bit.

• First choose a flat based bullet, and set the seating depth to zero. That makes GRT use the Case volume only for the fill ratio calculation.
• Second enter the case volume in grains of H2O.
• Third enter the weight of powder in grains to fill the same case to the top. Since the case is full to the top, the case fill ratio must be 100%.
• Now adjust the Pcd value until the Results shows 100%.

Bingo, you now have the Pcd of the lot on hand.

For rifles, there is a way to measure Pcd with a any bullet as long as you have a fired case that the bullet just slips through the neck.

You still need to know the fired cases volume in grains of H2O (yes, it can be done in Metric as well). You also have to have the dimensions of the bullet entered into GRT as well including and tail measurements. With this known case,

• fill the case with powder to the neck/shoulder junction, and
• place the bullet on top.
• Press the bullet home moderately.

Now measure the COAL of the cartridge. Enter that into GRT. Then adjust the Pcd until the fill ratio in Results shows 100%.

There is a least 5 methods to do the same thing. This last method compensates for any powder than can not rise to fill the air space between the bullet shank and case/neck walls.