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Old 09-01-2012, 14:42   #106
Counting Beans
Join Date: Dec 2008
Location: Boise, Idaho
Posts: 3,241
Originally Posted by TX Archer View Post
Thanks for taking it as it was intended. So what flattens primers? Pressure, right? How could the pressure from AA #7 flatten the primer but still remain at a safer level than another powder that did the same thing? It just sounds like myth to me, luckily a myth that isn't too widespread.

The primer condition from the photos is consistent with what I have observed using Accurate no. 7 & 9 (A7 & A9) accross a wide variety of charge weights. Flattened primers might be an indication of excessive pressure but not always.

I and others have noticed that with LPPs, A7 & A9 seem to flatten primers a bit extra no matter the charge. It is subtle, but a bit more than what I have observed with other powders. GT user Yondering on another thread hypothesized that because A7 & A9 granules are so tiny, they work down through the flash hole and completely fill the primer area voids with powder. Seems to make sense: more compustibles in the same volume of area could cause more pressure on the primer itself. I am not sure.

Whatever the reason, I have done a couple dozen different workups with various lots of A7 & A9 and this seems to consistently be what I have observed. Starting charges to max charges: primers are a little bit flatter with these powders than with others. They look just like the 2nd from the right case in the OP's photo.
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