[Unclenick]

AL45,

Western Powders (Accurate and Ramshot) have the only sites that give density information. They have both VMD's and a bulk density and tolerance for each powder. That tolerance can be as high as ±5.6% in some instances. This tells me Lee's VMD tables and even the VMD's that Western itself gives cannot be counted on to throw the same weight from any given dipper one lot to the next. You have to pick a Lee dipper and check. With spherical propellants each lot should be pretty consistent. With stick powders there can be transportation settling, though, so I would double-check every container with them, even if the lot number is the same.

I don't see any reason to believe other maker's bulk density variation is any different. This may explain why the Lee tables usually throw low. They probably evaluate VMD in a way that favors the high end of the density range when they know it. That way you don't get fooled into throwing a high charge with one of their dippers by mistake. Just keep verifying VMD's and you'll be fine.

Some benchrest shooters find powder dispensed by measures to be more accurate than weighed charges. This has to do with the dynamic interplay of packing density and burn rate. Weighing controls how much potential energy you put into a load, but packing density affects how quickly it can be provided by altering its burn rate. By fixing the volume, the powder measure at least partly compensates for density variation by adding more charge weight when tighter packing will make the powder light up more slowly.

If you really want the maximum control, you have to zero your scale with a primed case on it, dispense powder into it from a measure, then weigh it to see if you dispensed your target weight or not. If not, dump the charge out, make sure no grains are left behind, then repeat the process until you get the exact charge and density simultaneously. It's a big waste of time in most applications, though I have done it for load work-up purposes. It is a waste of time if your cases do not come from the same lot, are not all trimmed to the same length and not all weighing within about 1 grain of one another. Otherwise the difference in their internal volume will likely swamp out whatever value all that charge dispensing trouble you just went to had.