Knowledgebase: Powder Handling
VMD explanation
Posted by on 20 October 2011 04:07 PM
The Volume Measured Density (VMD) of a powder is the volume in cc's (cubic centimeter) that one grain of powder occupies. This can be used to calculate the dipper, disk cavity or powder measure setting required to obtain a desired weight of powder. The powder companies provide a VMD number or value for each type of powder. If you multiply the number of grains you wish to dispense times the VMD value the answer is the theoretical volume in cubic centimeters that are necessary to hold that grain weight of powder. Or grain weight x VMD = cubic centimeters. You can find the Powder VMD's by clicking on instructions at our website (www.leeprecison.com) and scrolling down to the bottom of the page and clicking on Powder VMD's. Once you know the number of cubic centimeters it takes to hold the powder charge you wish to dispense you can choose the proper disks. You choose the disk combination that is closest in size to the value of the formula without going over. If you have a scale check the weight of the powder charge dispensed by the disk combination.

Example:

If a powder has a VMD of .1064 , and the desired charge weight is 4 grains, 

4 x .1064 = .4256, or . 43 cc's 

This would translate to the .3cc dipper, (because the next larger one is beyond.43 ccs) the .43cc disk cavity, and a .43cc setting on the Perfect powder measure.

We attempt to keep a current list of newer powders and their VMDs on our instructions page on the website at: http://www.leeprecision.com/cgi-data/instruct/VMD.pdf

Determine a VMD on your own 

Using any setting on your powder measure (preferably a whole number), drop a charge of the powder you wish to determine the VMD for. Weigh the charge. Divide the measure setting you used to drop the charge by the weight of the charge. The result is the volume (cc) of a single grain of powder (VMD)

CC setting (powder measure setting)
--------------------------------------------------- = VMD (volume in cc's for 1 grain of powder)
Weight of the sample

It is very important that you repeat this process with any new container of the same powder because the powder companies allow themselves a 16% tolerance between batches. This can result in over charging if you work from the same setting and the next container of powder you get is more dense.
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