Perfect Powder Measure and VMD

[gonoles_1980]

As a step I added to make sure I set the scale correctly and to save me time setting the Perfect Powder Measure, I starting calculating the volume by using the Lee VMD*Grains to get the volume. This is the second time I've done it and I've been off by quite a bit. Is this normal?

N320 6.4gr
Lee VMD: .121
My Calculated VMD: .142 (17% off)

Titegroup 3.5gr
Lee VMS: .085
My Calculated VMD: .126 (that's off 48%)

I zero'd the scales, then used the Wilson Scale weights to verify.

I know at the bottom of the instructions it says numbers are approximations, calibrate your powder. But I would have expected closer results, at least within 10%.

 

[BigBore45]

I'm not sure i follow. the vdm factor is to select a CC measurement for the appropriate disk(s).

Example: Titegroup 3.5 grains

Titegroup vdm Factor.0847

Charge weight: 3.5 grains

.0847x3.5= .29645 lets round that up to .30

So you need .30CC disk hole to drop 3.5 grains or Titegroup.

or a .30CC dipper.

Why would you want to do this in reverse? All powder varies from lot to lot. i have some titegroup that was right on and others i have had to size up 2 holes on the disk. that is what the scale is for or you can get an adjustable charging bar. the bar works like all other powder dispensers, just screw the adjustment screw in or out to decrease or increase charge.

Here is one at midwayusa, there pretty cheap.

http://www.midwayusa.com/product/15...stable-powder-charge-bar?cm_vc=ProductFinding

 

[mstreddy]

GoNoles, if you are using the Perfect Powder measure, not the disk type, then you don't really need to worry about the VMD. Just set up your scale, adjust the PM, and you are good to go.
Trust your weights, you will be fine. Just remember to zero the scale appropriately.

 

[gonoles_1980]

mstreddy I am using the powder measure. I had been using it just like you're suggesting. I'm just looking to one more safety check for the scale since I almost blew it a couple weeks back using a 1gr instead .5gr weight when I adjusted the scale. I've since added back in zeroing the scale, that way, if I have to adjust with the weights more than a smidgeon, I know something is wrong.

Some other folks mentioned trusting the perfect powder measure. So I figured I'd add that in for a double check. Using the micrometer arm on the side it gives you the volume in cubic centimeters. Reading the Lee instructions, it provides a VMD (but then tells you it's probably not accurate for your current batch of powder). So I'm just trying to determine the cc value to set the meter at to throw the powder. When I weight it, it should be close. If it's way off, then somewhere I made a mistake in weighting (after I calibrate for the current powder). Just a double check.

Scale Validation Process
1. Zero scale
2. Check one set to closest .5 weight for my powder (Titegroup example is 3.5), check the 3.5 weight, there should be no, or extremely little adjustment to the scale.
3. Set perfect powder measure to expect cc level, the powder thrown should be within a grain or so of the scale, I'll adjust according. If it's off by a significant amount, I made a mistake in setting up the scale somewhere.

BigBore45 the issue is the Lee instructions VMD says the .296 is the expected cc measure for the powder measure to get 3.5gr of Titegroup. However, it had to be set at .44 for me to get 3.5gr of Titegroup. I expected it to be closer, I will use the .44 in the future for this current batch of Titegroup. I was hoping for two things, one a double check of setting the scale and two, speeding up my adjusting the dial on the micrometer arm in fewer than the 4-6 times it takes me now.

 

[Dudedog]

Yes
As stated VMDs vary may vary lot to lot. I have found some powders to be really close and some way off. (don't recall see any that were less than listed, but it is possible)
For example Unique is listed as .1092 but woking by what my two scales (Frankford DS750, RCBS 5-0-5) show with different disk sizes my 2 lbs from different lots were closer to .132 (about 30% difference here)

So I don't know if triying to correlate weight to cc as a check is going workj well for you.
Some measures don't even have cc marked on them.

Zero the scale weigh some check weights adjust the measure to throw the desired weight and check charges as often as you feel is necessary.

These are some inexpensive check weights.
http://www.amazon.com/American-Weig...&qid=1419388761&sr=8-3&keywords=check+weights
They are in grams not grains so if you don't have a digital scale you will have to make a conversion chart. The tweezers stink but the weights are ok.

 

[Potatohead]

Yea that VDM crap is always waaay off. I just screw around with it til I get the right charge. (pro auto disk)

 

[berettaprofessor]

What Potatohead said. I use the calculations if I need them and only to find a starting cavity and then adjust.

 

[gonoles_1980]

Dudedog and Potatohead, I could go back to that. Just experimenting to see if I can have a backup double check. I'm pretty anal on the measuring.

I'm guessing, I will have to change the values for each new batch of powder, but if it gives me a "Yeah, it's in the range" check, then I'm ok with the extra upfront time. I have to admit, when a couple of weeks ago I used a 1gr vs .5gr weight to calibrate my scale it's made me even more paranoid. I will say, the good news, this was the 3rd mistake my process caught over the last 18 months, so that's a good thing.

 

[mstreddy]

GoNoles,

What you are doing with the zero, check weights, charge weights is fine. You have a check built in with the check weights. No need to add another step with the VMD with the variability that they introduce. Trust the PPM, trust your process, you will be fine. You see how the check weight vs scale setting showed you had a mistake somewhere...

BTW, which scale are you using?

 

[Rule3]

Calculating VMD is about as useful/useless as using the printed values that LEE gives you. It is a waste of time.

Drop some powder weigh it and trial and error adjustment of your powder measure (regardless of the make)

If you have a good scale and check weight all is well. VMD tells you nothing to verify your individual powder charge.

 

[A Pause for the Coz]

I think LEE's VMD is set low on purpose. Same with their load data.
Its always lower than published loads for any specific bullet.
I have not seen any higher than any one else s any way.

I dont blame them ether. LEE caters to the new re-loader.
If you follow their data you are guaranteed to be in the safe range for what ever cartridge your loading for.
Helps keep new guys safe and keeps them out of court.

 

[RandyP]

The low posted data 'almost' ensures that the first timer will not hurt themselves and begin the hobby safely. Same goes for using the data to select one of their 'scoops' which will indeed produce a safe, workable load, though most often lower than predicted, again safety first.

I too disregard the charts and use the trial throw-weigh-adjust method. For ME an inexpensive digital scale provides and easy to use 'accurate enough' means to that end for my mid-range loads.

 

[higgite]

I agree with the consensus opinion here. I only load 2 powders, one for rifle, one for pistol. If Lee's powder chart is as far off on other powders as it is on the 2 that I use, I don't even know why they bother to publish it.

 

[Potatohead]

I don't even know why they bother to publish it.

For real.

 

[gonoles_1980]

Thanks guys, I have the Lee Safety Scale. I'll do the CC measure as an experiment for a while, just to see how it works out with my own measure with hope's it'll save me a little time in getting the powder dispenser to throw a good load quicker, I figure I can use that as my starting point to get the right throw out of it.

mstreddy - you're right, my process is working, adding in the zero scale at the beginning is probably the only real step I need.

 

[Rule3]

The calculation of VMD is primary only for setting the LEE PPM micrometer, It is an exercise in Futility.

It may get you close but you still need ti fiddle and adjust. You can just do that and come up with the correct weight.

A suggestion is to invest in a scale that is easier to use and work with. The LEE is a PITA. First thing I got rid of. Save yourself some headaches

A quality reliable easily to use scale is the most important tool in reloading. Not a cheapo electric one either.

The Dillion eliminator and the RCBS 505 are the exact same scales made by OHaus.(different color)

http://www.grafs.com/retail/catalog/product/productId/3018

http://www.grafs.com/retail/catalog/product/productId/12887