Good to know . I am shooting up a bunch of my Dads .38 and .357 loads and some of the .357 has flattened primers . They are accurate and he matched all of the brass . They extract fine . Just I noticed the primers are flat .

Just picked up a pound of H110, some coated hard cast 158gr bullets, and some magnum primers.......going to start working on some heavy magnum loads for my GP100 .

Well, I was able to dial in some good loads. I started with 15.0g of 296 and worked up to the max of 16.7g.  I was surprised to see flattened primers even with the starting loads of 15.0 grains of powder. But the cases all dropped free from the cylinder...even up at max load they still dropped free. I did load up some 17.0 and 17.2 loads just to see what they would do.....and they still dropped free from the cylinder, but my velocities were not any higher than at 16.7gr......around 1350 fps out of my 4" GP100.  I settled with the 16.7gr loads and loaded up a few hundred to play with.

I'm assuming I maxed out on velocities because of the barrel length......??