Herco charge density

[DrDoom]

I was evaluating some Herco loads for 9mm. I am getting .88 Lee Auto disk dropping 6.4-6.5gr. I am seeing loads that list up to 7.8gr as the maximum load. 6.4 grains fills the case to about 90%. It doesn't seem like 7.8 grains would fit. So I'm a little confused as to what to do, I'm thinking that there is some wrong with the data? I'm using powder that is probably 20+ years old. The data is from Speer #11.

 

[Ron Blain]

Alliant Herco has a VMD (Volume Measured Density) of 0.1122. VMD is the volume of one grain of gunpowder in cubic centimeters. To find the volume of a powder charge, multiply the grains of powder by the VMD so with that in mind if we want a 7.8 grain charge we get .1122 VMD * 7.8 grains = 0.87516 or roughly .88 is close enough and what you have. One problem we have is that the published VMD is not always an accurate number, even though powder makers try to maintain a 16% tolerance between lots. Rather than take the charted VMD as accurate if you have a scale we can manipulate the numbers. Try this:

Determine a VMD on your own using the 0.88 cavity

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) use 0.88 cavity
--------------------------------------- = VMD (volume in cc's for 1 grain)
Weight of the sample (in grains)

That should give you an accurate VMD number and apply that. The only loading I see in the Speer #11 mnual for 9mm using a 95 grain bullet call out a min load of 7.0 Grains and a maximum load of 7.8 grains. They do not show the maximum as a compressed load. Typical 9mm Parabellum has a case capacity 0.862 cm3 or (13.30 gr H2O). The Speer #12 drops the data for Herco entirely. The general case capacity does not account for bullet seating,

Ron