powder VMD

[horseman]

The discussion on VMD on another post started to wake up some brain cells so I thought I would continue with the VMD discussion on a new post as I was afraid I'd "muddy" up the one where we started the discussion although it does apply. I hope I can do this without confusing everyone with my "thinking".
The first thought I had when this started sinking in was the statement "always rework your loads when you change to a different lot number of powder as it can vary by at least 10%". I'm sure you all have read this before. I do this with bottleneck rifle but not pistol stuff as pressure signs are difficult to really read in straight wall pistol rounds. NOW, that statement makes sense to me because the density changes lot to lot. No, I never put it together in that relationship. So now, MY interpretation is, (please correct me if incorrect) that the denser the lot of a given powder the more "energy" it will produce at the same charge weight as a "less" dense lot??? Still not sure how I'll use this information, I'm a slow learner by nature but I'm sure something will eventually come to me... More reading needed to turn on the light.

Would be easier, for me, if reloading manuals would use the VMD of the powder lot used when they worked their load information so we would have a baseline for that load. Yes, I know that's why we "work up" loads, but it would be nice to have that "baseline" just the same. Perhaps I'm over working this but when I learn (I think I've learned) something new at my age I get pretty excited....

[Bagarocks]

I'm at work but I have a formula, pretty sure its Lee's. That let's you figure out the size of 1gn of powder then mathematically figure out the vmd. I did it with BLC 2 powder and it was spot on.
Unless some one posts it today. When I get home tonight I will post it. I don't remember where I got it. Maybe Lee 2nd editon?

[horseman]

More thinking on this subject . Say I have "worked" up a load of 10 grains of xyz powder to give me a velocity of 1000 fps and this powder has a VMD of .12345. I buy another lot of this same powder and come up with a VMD of .12445 which would make it more dense. Correct?? If I take this lot of powder and weigh out the same 10 grain load it will be a "hotter" load ???. If this is the case I've been reading a lot of opinions on the "usefulness" of VMD from reloaders that don't understand the concept. Maybe I don't either. "They", only look at it as a way to set a "number" on the measure to get "close" and then just weigh to whatever number they want on the scale. OR...is 10 grains still 10 grains just less volume...Overthinking this again ????

[larryw]

Yea, confused me also Hoesrman..

[Ranch Dog]

More thinking on this subject . Say I have "worked" up a load of 10 grains of xyz powder to give me a velocity of 1000 fps and this powder has a VMD of .12345. I buy another lot of this same powder and come up with a VMD of .12445 which would make it more dense. Correct?? If I take this lot of powder and weigh out the same 10 grain load it will be a "hotter" load ???.

No, 10-grains is 10-grains, the charge behind the BOMB. If you are weighing charges, VMD is not a thing.

If you are using a CC or CI delivery system, you are not weighing charges; you are dropping volume. That's why knowing the VMD of your powder important. If your VMD is LESS than the spec, you will be dropping a heavier charge. In that it is heavier, the power of the BOMB will be greater. Of course, it is easy to weigh the charge and know that, but this conversation started in the other post with the age-old question as to "why my disk isn't dropping what Lee's chart said it would."

This is why Lee's volume delivery system instructions say to weigh Max loads. If you don't know the exact VMD of your powder, there is a 50/50 chance that using a volume measure to drop it will result in a higher than expected charge.

Probably 99% of us here on the forum own a scale. We are not all reloaders. Lee has sold a lot of Loaders and press kits that depend on volumetric charges. Progressive presses come with such, but no scale. I know guys that have bought them and never added a scale. Hence, the warning. Cavity down from max if you don't know.

I've used QuickLoad and my pressure trace equipment to explore this in-depth. QuickLoad does a great job of showing that a change in the density (specific gravity) does not change the BOMB when weight is the common denominator.

[Ranch Dog]

If your VMD is LESS than the spec, you will be dropping a heavier charge.

Remember we are talking about a fixed cavity. If the product is less dense than the spec, it takes more of the product to fill the fixed cavity. This applies to powder in a disk cavity, fertilizer in a spreader, or grain in a bin.

Honestly, I work more complex product density vs. metering device calculations on my seeders and spreaders than I do with Lee's delivery systems.

[horseman]

If your VMD is LESS than the spec, you will be dropping a heavier charge.

Remember we are talking about a fixed cavity. If the product is less dense than the spec, it takes more of the product to fill the fixed cavity. This applies to powder in a disk cavity, fertilizer in a spreader, or grain in a bin.

Honestly, I work more complex product density vs. metering device calculations on my seeders and spreaders than I do with Lee's delivery systems.

Got it Michael, thanks, I kinda figured that out as I was staring off into space thinking more on the subject. The missus thought I was in a coma ...but the confirmation is appreciated. Dodged another bullet, so I'll just get back to my regular scheduled program...I weigh everything but do use the VMD chart when using Lee measures to get "close".

[larryw]

Finally?????? A straight from the hip, no BS, no fancy run around explanation of VMD stuff.
Thank you RD. Wish someone would have said those same words that Same way to me
many moons ago. As Horseman said, Thanks RD for the conformation.

[RBHarter]

For the sake of shadows and confusion ..........
The weight by volume change for powder density , heavy lot weighs more in a specific measure chamber of volume , can also go the other way with light lots . .5 gr isn't a big deal over under in an 06',300 WM , or 458 , 45-70 for that matter but .2 over/under in a 380 or 9mm where the load window is only a half grain can get pretty exciting . I had an Auto Disc and it dropped way light with the chart disc in my old Unique like a full grain light on 6-9 gr loads .

The next step issue that can happen is without baffels in the hopper , not so much on Lee measures but more especially with shotgun presses and measures like the Uniflow that hold a full pound or more powder can weigh heavy full and light towards the bottom . A simple baffel will correct most of that or reduce it to .2 run out top to bottom .
What happens is the weight of the powder causes a denser fill of the volume chamber more so when it is coupled bumps or vibration on a bench . A baffel creates a false hopper of limited volume over the opening for the measure .

I use the Uniflow set up in a normally closed arrangement so that I have to raise the handle to open the chamber and it dumps on lowering . This has allowed me to drop 200+ charges of Unique tray changing 9mm ,38/357 , and 45 ACP and Colts to .1 random QC & 1/20 scale checks with Unique and drop 45-65 gr drops of 4350 and H1000 consistently .2-.3 light and 19-23 gr of H322,4198,4895 at -.1 to 0 for up to ...... I guess a full hopper , 250 ea 223 most recently after checking set up and drops at 5,15,30&50 I was comfortable with dropping the rest of the lot with a visual inspection an 1/25 just to be sure .

With any measure doing whatever trips the measure whether it's you or a pull chain or striker bar whatever is done on the bench has to be done the same every cycle . If you bump or double bump a manual do it the same each throw , settling is as big as hopper load and baffel load .

I'm an unabashed scaler due to $50 inconveniences that could have easily been catastrophic failures in my youth 40 odd years ago . It took me years to have enough faith in measures to use them for more than a get close and trickle tool . Anything that needs real accuracy still is .

[Macd]

Good topic and discussion. Just to "muddy" the waters a bit this is straight from Lee's Second Edition (Para 2, Page 66.)

"Bob Hodgdon of the Hodgon Powder Company told me that quickness and density are equally important for a proper powder charge. And they work very hard at maintaining a proper relationship between the two. They believe that a powder that may be on the dense side of tolerance should be on the slower side of the quickness tolerance. The logic being that the charge will be safe if either weighed or dispensed by volume. You see, if you weigh your charge, the pressure will be on the low and safe side because the quickness is slower. If you use a volume measure the charge weight will be greater than it should be according to the weight and the pressure will be right where it belongs."

I know Richard Lee is making a pitch for his volumetric measures but there is an interesting suggestion contained in this reported conversation. There is room for a powder company to adjust for density differences between powder lots by adjusting the burn rate to compensate. This could be accomplished with modifying the type and quantity of the deterrents used. I don't know if they do this but one has to wonder.