Zendude
Member
I’m guessing that Lee doesn’t want there to be any chance of throwing a heavier charge than the chart shows for liability reasons.
Lee Powder Measure
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kerreckt
Member
I have found the VMD to be pretty accurate. It always gets me into the ballpark. I then fine tune. I have never seen the large discrepancy you mentioned. I only use my PPM for the IMR "logs".
Dudedog
Contributing Member
refuse2bafool
Member
I have posted this a few times...
VMD is a very clever idea, but you need to determine a specific one for each container to take full advantage of the concept.
You will often get lighter than listed charges when using the auto disk. This is by design. Density of a given powder can vary up to 16%. The values on the tables are at the high end of density for that powder, which is the low end of VMD. If someone is foolish enough to load without a scale, the actual load may be less than the target load, but never greater. If you want to get very close on your first try you should calculate the VMD for each container of powder.
Take a dipper or other known volume of a powder and weigh it. Now divide the cc by the grains. That’s your VMD in cc/gr for that batch of powder. An example…
2cc/15gr = 0.1333cc/gr VMD
To get a four grain load: 4.0gr x 0.133cc/gr = 0.53cc. Pick your cavity or adjust your charge bar accordingly.
VMD is a very clever idea, but you need to determine a specific one for each container to take full advantage of the concept.
You will often get lighter than listed charges when using the auto disk. This is by design. Density of a given powder can vary up to 16%. The values on the tables are at the high end of density for that powder, which is the low end of VMD. If someone is foolish enough to load without a scale, the actual load may be less than the target load, but never greater. If you want to get very close on your first try you should calculate the VMD for each container of powder.
Take a dipper or other known volume of a powder and weigh it. Now divide the cc by the grains. That’s your VMD in cc/gr for that batch of powder. An example…
2cc/15gr = 0.1333cc/gr VMD
To get a four grain load: 4.0gr x 0.133cc/gr = 0.53cc. Pick your cavity or adjust your charge bar accordingly.
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I have wondered if on the user end, the powder is more fluffed, from movement. Where Lee, or who ever compiles the list, may let their powders settle to the most densest form. But that is only my assumption.
refuse2bafool
Member
It is not really a matter of "settling". The variation is intrinsic to the manufacturing process. It's explained on Lee's website. You can buy a set of dippers for $12 and determine VMD for each container per above. It will save a lot of frustration; at least it did for me.
daboone
Member
from Titan Reloading website
VMD Explanation
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.
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.
Lee attempts to keep a current list of newer powders and their VMDs on their "Instructions" page of the Lee Precision website.
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)
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.
VMD Explanation
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.
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.
Lee attempts to keep a current list of newer powders and their VMDs on their "Instructions" page of the Lee Precision website.
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)
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.
refuse2bafool
Member
daboone, Is there a away to make that a sticky or something? This a contantly recurring topic and I've posted the explanation a number of times. I am not enough of a power user of the site to know the options.
daboone
Member
Not me, my post count barely makes me a member. Beside very few have PMs that take VMD into account . Beside that info is included with Lee measures. The info above was a cut and paste from Titan Reloading website.
Beside very few have PMs that take VMD into account . Beside that info is included with Lee measures. The info above was a cut and paste from Titan Reloading website.
refuse2bafool
Member
Not me, my post count barely makes me a member.
Yeah I got that it came from Titan from the big bolded letters
A lot of people use LEE powder measures, and I think if very few used VMD we would not see this question pop up again and again. But like you, I don't post a whole lot. Lee includes this info with the charge bar, but not with the Pro Autodisk.
Oh well, at least we tried to share the wealth.
jaguarxk120
Member
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Hey coins are coins, I think there are a number of reloaders
that use pocket change as check weights!
Usually they go by the name of "Lefty".
that use pocket change as check weights!
Usually they go by the name of "Lefty".
I used new coins when I figgered it was necessary. But, IMO, home reloaders' powder measures/scales don't have to be dead nuts on with regard to exactly matching a known weight of a certified, to within .01 grain certified scale. What I mean is if my scales weigh within .3 or more grain of a certified laboratory scale, but is repeatable, no problems (but I'm sure the difference will be much lower, mebbe .1 to .2 grain). I always start my reloading with starting loads so f my scale says 8.4 and the certified scale the testing lab used says 8.1 my loads will be safe. I don't know anyone (except "Lefty") that starts loads out at max. and I know what to look for to keep my loads safe. Same if my scale says 8.0 but the manual says 8.5. The main need for a home reloader's scale is repeatably. Every time the scale is used it must read/weigh the same. If a load in my manual(s) says 47.5 gr. and my loads are a consistent 47.8 (both well under max. reported loads) what is the problem? I can if necessary vary my loads to suit the gun...
I am not advocating sloppy reloading, but I believe some reloaders get extra OCD, go way overboard when it comes to powder charges and fret over their scale's .01 grain accuracy of powder charges to exactly match what is in their manual...
I am not advocating sloppy reloading, but I believe some reloaders get extra OCD, go way overboard when it comes to powder charges and fret over their scale's .01 grain accuracy of powder charges to exactly match what is in their manual...
kmw1954
Member
VMD????
I use both a Lee Auto Disk measure and a Lee Auto Drum measure. I also have the VMD charts that come with Lee dies and Never use them. When I start each reloading session I weigh probably 15 to 20 drops to get the measure and the scale to settle in. With the Drum I then set the charge weight and drop 10/15 more just to verify. With the disks I have used then enough with each of the powders that I use that I know and have recorded how much each cavity throws with each powder. I even mark the cavity number on the finished labels and in my log book. Also over time I have found that the weights do not stay consistent from one loading session to the next and I attribute that to environmental factors such as temp and humidity. It can very by as much as +/- 0.2gr with some powders but is still very much within my load range.
I use both a Lee Auto Disk measure and a Lee Auto Drum measure. I also have the VMD charts that come with Lee dies and Never use them. When I start each reloading session I weigh probably 15 to 20 drops to get the measure and the scale to settle in. With the Drum I then set the charge weight and drop 10/15 more just to verify. With the disks I have used then enough with each of the powders that I use that I know and have recorded how much each cavity throws with each powder. I even mark the cavity number on the finished labels and in my log book. Also over time I have found that the weights do not stay consistent from one loading session to the next and I attribute that to environmental factors such as temp and humidity. It can very by as much as +/- 0.2gr with some powders but is still very much within my load range.
badkarmamib
Member
No, they are not the perfect check weights. But, I couldn't find a set of affordable (<$200) that didn't have bad reviews. As @mdi stated, I start low, and work up. I keep the same dime in with my calipers, and only use it to verify that my beam scale is level compared to where I had it set the time before, when I used the same, known, safe load. This is part of the reason why I refuse to share my load data with others. I know that my loads are safe in my firearms, when loaded with my equipment, but not necessarily for anyone else.
thomas15
Member
Show off!
refuse2bafool
Member
You are basically determining a volume to weight ratio by trial and error. That's all VMD is. The problem is that if your next batch of power has a different density then your recorded data may not be accurate. To me it seems it's a lot easier to determine VMD for each container and use a bit of basic math to predict cavity size as described above. On the other hand, if you are more comfortable and confident with your method, that matters more than a small efficiency gain. I have a lot of confidence in VMD, but still check weights at the beginning of each loading session, even if I have loaded the night before. That's my security blanket.
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