Powder Lot Effect

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Jim Watson

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A while back, in the lull between the Obama Component Panic and the Obama/Clinton Component Panic, I bought an 8 lb keg of HP38, my usual non-magnum pistol powder.
I finally used it up, but that was OK, I had a single can acquired swapping components around during one of the panics and a whole new 8 lb keg bought after availability and price improved.
I first used the single can with no discernible difference in powder measure setting or velocity.
But then it played out, so I thought nothing of just going straight to the current keg.

I check weigh powder on the Dillon every time I fill the primer tube and any time there is a funny sound or feel.
Lo and behold, powder charges seemed a bit light so I checked some more. Confirmed. Not much, but you can tell a small difference with a "spherical" powder, and I was sure I was seeing 0.1 or even 0.2 grain dropoff. I tweaked the Mr Dial to get back to where I was with the previous can and carried on. It will be interesting to chronograph and see if there is a difference and should I have changed to make weight or stayed with the same volume.
 
I checked IMR 4198 and Alliant 2400 by volume, different lots. Big difference in weight.

IMR 4198 ( 18.5 gr vs 19.6 gr.) and Alliant 2400 (13.0 vs 13.6)

No chronograph to check velocity difference.
 
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I generally find I have to tweak my powder measure a little to get it to throw the same weight charge when starting up a new loading session for a particular cartridge. Changes are both up and down and generally a few marks on the micrometer head of the powder measure. It happens within the same lot of powder and lot to lot. Loading sessions are separated by several months or maybe a year.

I've seen small differences in velocity but not a significant difference and possibly attributable to atmospheric changes.

I figure moisture changes in the powder are a likely cause. Maybe the way I get the powder to settle when filling the powder measure.
 
Jim Watson said:
I check weigh powder on the Dillon every time I fill the primer tube and any time there is a funny sound or feel.
Lo and behold, powder charges seemed a bit light so I checked some more. Confirmed. Not much, but you can tell a small difference with a "spherical" powder, and I was sure I was seeing 0.1 or even 0.2 grain dropoff. I tweaked the Mr Dial to get back to where I was with the previous can and carried on. It will be interesting to chronograph and see if there is a difference and should I have changed to make weight or stayed with the same volume.
Click to expand...

I think only blackpowder is consistent by volume, as you know, reloading manuals and reloading data is in weight (the force on an object due to gravity). That's all the loading companies will guarantee, that the pressure curve of the powder lot you have is +- 5% or +- 10% of the pressure curve of their standard lot, by weight. They blend the stuff, fast lots with slow lots, to get the average down to their standard. They don't guarantee density, they don't guarantee volume, and it makes a difference. Seeing a difference in velocity with 0.1 or 0.2 grains might take a big sample size, based on my 32 round averages. My Chrony only goes to 32 rounds for statistical calculations. I frequently see difference in average velocity, SD, and ES's, out of the same gun, on the same day, with the small ammunition.
 
For pistol for me for the most part when adjusting the measure for a new lot of powder to get the same weight used previously the velocities have been pretty close for multiple powders. Sometimes lots differ slightly in burn rate, but they do a great job of keeping it very close from lot to lot. I always adjust to get the same weight on a new lot of powder. I had two lots of Universal 10+ years apart that were identical, but most times I have had to adjust the volume to get the old weight, usually not much though.
 
I sure would like to get a plant tour and see all this back blending going on.
I worked in fertilizer R&D and if we couldn't hold our analysis a heck of a lot closer than 5%, somebody was going to get chewed out.
 
Nope.
Only explosions at my agency were intentional, explosibility studies on new blends with a lot of nitrates. Maybe three or four pounds.
 
While I don't know how much truth there is to it this short article on VMD Explanation does mention:
It is very important that you repeat this process with any new container of the same powder because the powder companies allow themselves a 16% tolerance between batches. This can result in over charging if you work from the same setting and the next container of powder you get is more dense.
Click to expand...

While powder weight is just that, a measure of weight, the volume for a given weight will be subject to change. How much will that effect pressure or muzzle velocity? Over the years I haven't seen that much if any change to speak of.

Ron
 
I have found some are pretty consistent lot to lot volume to weight some not as much. same thing burn speed wise, the different lots of some powders I have were close, other maybe 5-10% burn speed difference.
Others powders varied about 5% volume wise for the same weight.

4 different lots of WSF were all to close to call weight/volume and burn speed, Universal seems good as well. Had three lots pof BE86 all close volume wise but on lot was .2gr hotter in 9mm than the other two.
Even though the tolerance is ok and allowed it might be interesting to start o list of one that seem good lot to lot.

Note: some of Lee's listed VMDs are close some are off by quite a bit.
For example they list Unique at .1092, my jar was much fluffier at .132 measured
 
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This thread makes me think of Promo vs Red Dot powders. They say use the Red Dot load data for Promo, but that the volumes could/will be different. I think I remember reading that even the Promo volume will change lot-to-lot.
 
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