I use the VMD as a safety check

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gonoles_1980

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Actually the converted CC's. I have measured it in my Perfect Powder dispenser and documented. Yesterday it helped me realize I set my scale to 7.2 instead of 8.2, because using the CC measure on the dispenser, I was getting about a grain too heavy. I know if I am off by more than a 1/10th of a grain or so, my scale is not set right.

My question is, why is the Lee document containing VMD's that came with the dispenser so far off from what I actually measure. On average, my measured VMD's are 20-50% higher than what the VMD on the Lee document is. I would have thought they'd be closer.
 
A CC is a cubic centimeter. I don't know what you mean by "converted CC".
You will always get different weights with your actual measurements than what is published in Lee's VMD guide because of several factors including, but not limited to, different powder lots, different scooping techniques, inconsistent scooping techniques and Lee's use of low-end calculations as a "safety factor" to purportedly avoid liability lawsuits. You will note that in the VMD instructions it states that their VMD figures are a "guideline only" and are not intended to be exact. You are expected to verify your own charge weights.

Do not use the VMD figures to calibrate your scale. Use a check weight.
 
I am not a very big fan or supporter of using the dippers for charging a case, at least not the dippers alone and here is why. The below data was collected using a dipper and H335 powder.

Dipper%20Test%203.png


The VMD is not always reliable for a number of reasons the least of which is that powder VMD (Volume Measured Density) varies from lot to lot of manufactured powder and while manufacturers try to stay close they can vary something like 16% was my read. I came up with that number from this read on the subject. IN my little science experiment I tried to maintain uniformity in each dip and keep my actions consistent. The above numbers pretty much run with what Splattergun mentions above.

When I set up a powder throw like the RCBS Uniflow or the other equivalent versions I set it up against a known good scale. I throw several charges getting things set and once I am throwing uniform charges I run with it, checking every 10 or 20 rounds to make sure I am consistent in my charge weight. Anyway, the deviations you are seeing based on VMD are no surprise.

Ron
 
Response to Splattergun
The converted CC was just my short hand way of saying VMD converted to CC. I don't use it to calibrate the scales, I use it as a safety check only. I have measured the CC's from the Perfect Powder dispenser (on the arm that protrudes out, to see the CC level), and I've documented those values.

I first calibrate my scale at zero, then half way to my weight with scale weights (nearest .0 or .5), then at the nearest .0 or .5 to the weight I want. Making sure the scale is consistent.
I then set the CC on the powder dispenser based on the average of my historical recordings.
I set the scale to the weight I want.
I dispense the powder, then weight it. I should have to only make very minor adjustments, if any at all on the powder dispenser. If the weight is off by a lot, that means I set the scale wrong. In the case I had the other day, I moved from 8.0 to 7.2. This safety check caught that. I set the scale to 8.2.

I always verify my own weights, it just seemed odd that the Lee published VMD is different than what I get. My numbers come from what I have to turn the CC dial to, to toss the correct weight. I created the VMD from the actual weighted powder, not the other way around. I have read the the Lee instructions. I was just really curious as to why my measured delta was so different. Maybe theirs was geared to the scoopers an there is that much difference between a scooper and a scale.

Response to ReLoadon
I don't see those deviations in my calculated VMD, but then I created my VMD from the actual scale measurements. As I mentioned above, I set the arm dial on the powder dispenser to toss the correct weight. When that is done, I document the CC. I keep that value as a safety check only. I've never used a scooper (unless you count my coffee scooper and that is not overly accurate, but the coffee tastes the same).

If I understand both of your comments correctly, I'm going to guess Lee based their numbers on using a scooper, and probably used the low end to be safe (my theory only), and that's why their numbers differ from what I am calculating using the scale to create my CC value.
 
I averaged out dipper charges for some calibers as a SHTF exercise. I wrote them down. They won't win any matches, but they'd keep me shooting.
 
My question is, why is the Lee document containing VMD's that came with the dispenser so far off from what I actually measure.
When Lee put together the chart decades ago, they only physically checked a few powders to get a baseline. Then they used theoretical densities to calculate (mathematically) the rest of the chart. For those few powders, the VMD is perfect. For the rest, only approximate.

Your procedure is sound, use the VMD as a general guideline, then check on the scale.
 
Thanks ant's, there have been a couple of times, I've caught that I set my scale wrong using the VMD. If the scale is set right, I shouldn't have to rotate the arm dial much at all. If I do, then my scale is set wrong like I mentioned above (where I set it at 7.2 and not 8.2). Using the VMD showed it to be way off letting me know something was wrong.
 
VMD chart cannot always be accurate as compaction of powder changes things and when dealing with a powder that can be used in several calibers and range from 5gr to 25gr the compaction will show itself. The weight may be multiplied by 5 but the cc or volume it will be less.



With that being said measuring by volume is fine and can be very accurate that's how powder dispensers do it. As long as the weight is verified by scale your good to go.

When Lee set up the chart it knew this too. There is a reason that they say when using the dippers to never tap powder or shake as it would settle and compact.
 
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