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Old August 22, 2015, 05:13 PM   #3
Kosh75287
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Join Date: October 15, 2007
Posts: 822
The smaller the volume of powder involved, and the larger the grain size of the powder, the greater the potential for variation in charge from round to round. With the .380 ACP, you have a pretty tiny volume in which the powder may be placed. If you use a ball-type powder (say, W231, or AA#5), which typically meters very nicely due to the small granule size, I would expect the mass of powder from one round to the next to differ by very little, affecting velocity (thus accuracy) very little. If you use a flake-type powder, like Unique or Herco, which has the reputation to "meter like cornflakes" then there is more opportunity for variation in charge weight from round to round, with attendant variance in velocity, thus accuracy.

There are other factors at play, here, but this is the first consideration that occurs to me.

And sometimes, some powders are just not suited to use in certain cartridges. Alliant Unique seems to work in almost all pistol cartridges, while slower burning ones like Blue Dot or H110 (especially H110) are suited for use only in magnum-type cartridges.

There's a very good powder called IMR-PB, which works wonderfully in almost all low-pressure cartridges, but simply is not formulated to give top performance in the more modern calibers.
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