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I recently was switching loads on my PW 375 and noticed that the same PW bushing threw 32.5 gn of Blue Dot vice the 29.5 gn I had recorded on the previous reloading sheet with the same bushing. What happened? Why would there be that much difference between dropped weights using the same powder bushing?

To cut to the chase, it was two different lots of Blue Dot. One lot was the older Blue Dot packaging and the powder was bulky flakes with a dark grey/black color and not glossy. The other lot was the newer packaging with the powder being flattened disks (not flakes) with a shiny black color. Both had the blue dots characteristic of Blue Dot powder. Such an obvious difference in color and texture in the same powder was new to me.

I adjusted the bushings to get the correct throw weight and had no issues with the shells...all seemed normal.

I know that powder lots can vary in density/throw weights but 3 gn or about 10% seems like more that expected. It exceeds my experience with other powders of perhaps 0.5 gn difference between powder lots.

This post is to: 1) let folks know what I found, 2) ask folks if they have found similar differences in Blue Dot or other powders, and 3) ask if folks have found perhaps loaded shells without checking for differences in powder lot density and noticed differences in apparent pressure and recoil.

Any comments to the three items above are welcome and appreciated.
 

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I do not load Blue Dot for shotguns. But I did for handguns. I do not know the relative ages of the lots of powder you are dealing with but Blue Dot actually changed somewhat at some time. And Alliant changed the handgun reccomendations for it. For one thing Alliant completely removed its use in .41 mag. in their manuals and wrote a recommendation not to use it fro .41 mag. Of course that is the gun I bought it for. I think the only part of this that applies to shotguns is I have seen references to "old" Blue Dot and "new" Blue Dot at various times on the Alliant website.
 
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