Understanding the Science

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Last night I was reloading some 6.8 SPC using A2200 powder and came to the end of the 1998 lot of powder I had been using and switched to my new lot dated 2009. As per usual practice I emptied the hopper of the old lot and filled it with the new lot and to my surprise this new lot was .7 grains/2.5% lighter than the charge weight (28 grains in this case) for the old lot. Also, when I added powder to make up for the difference there was a very noticeable difference in case fill. To reconfirm, I emptied the hopper and put the remains of the old lot back in and it was right on zero again. The only other time I have come up with a difference between lots is with H335 for .223 loads, but it was only .1 - .2 grains heavier which is a no brainer for range fodder.

To the science of powder making, are there general manufacturing tolerances controlling the entire formula, or are the "explosive" ingredients held to an exact spec and the balance held within a "range" ? Then, do these variances effect burn rate, or just volume, or both?

Thanks in advance.

PS, I have already made up a ladder of the new lot to test.

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[DizzyJ]

I think powder can absorb moisture. Perhaps over the years the older powder has done this?

Of course as you mentioned, lots will vary as well which is why they always say to reduce your charge when starting with a new lot #

 

[gmerkt]

I've noted approx. half grain charge weight variations with IMR 4064, in powder that was approximately contemporary in lot manufacture. I'm not apt to catch this unless switching lots in the middle of my work. Best way to avoid this is to buy larger than one pound containers. Eventually, any size container is gonna run out, though.

Powder can also dry out with age. Which can effect weight. And energy content.

A cousin once gave me some H4198 and Unique that were about 30 years old. Which had been stored in cardboard drums. He lived in a dry climate. Later, I ran some tests between the 30 year old stuff and recently made product, using same charge weights. I don't remember the exact numbers now, but the results showed a loss of velocity in the old stuff by about 5%. So I assumed that as the powder dried out, it suffered a bit of energy loss.

 

[quneur]

OLD Accurate 2200 Data Powder & The NEW Accurate 2200 Powder

About 16 years ago I bought 8# of Accurate 2200 Data Powder in response to a closeout flyer that touted how good it was for reloading .223 Remington and 7.62x39. So for $48 ($6/pound) I gave it a try and they were right; I was very pleased. I’ve lost the data sheet that was supplied with the...

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