If my cases collapse like the ones pictured I use faster powder, heavier bullets and or more powder. The neck did not expand and seal the chamber, gas traveled back between the chamber and case before the case sealed the chamber. And then
the hot high pressure metal cutting gas got trapped between the chamber and case preventing the case fro expanding etc., and as a results; big dents. When a reloader 'almost' has it correct and worked out the case neck will turn black and carbon up. Again, a friend died, his wife gave a reloader close to 80 7 Remington Mag cases that he did not use so he gave them to me. The carbon on the necks had to be chiseled off. I then suggested we find the rifle because there was no way the neck of the case could expand when releasing the bullet. No one new who got the rifle; but we tried.
F, Guffey