Paul,
What your dealing with is brass that came from a box of Winchester “Win-Clean” ammo. When Winchester decided to make a reduced lead round they used a lead free primer. However, the new primer was not as hot as a traditional lead styfanate one and it wouldn’t ignite the powder in certain circumstances. (Like cold weather). To compensate for this they went with a larger diameter flash hole. This solution created a new problem, the larger flash hole would allow more gas pressure back to the primer, sometimes causing it to back out of the casing, locking up the firearm. (like when it’s fired out of a revolver). To solve this problem, Winchester engineers crimped the primer in place, like in their military ammo. Unfortunately, Winchester did not change the head stamp on this ammo so it’s impossible to tell without really looking at the flash hole.
Most of the brass that I buy comes from indoor ranges, and of that, I’ve been getting around 2% of this brass. It has forced me into some new culling procedures. First I look at all the head stamps and throw out the junk. (S&B, A-merc, etc). Then I set a decapping die in the press so it hits the shell plate as low in the travel as possible. This causes me to use more force on the arm of the press to deprime and I can feel if any of the casings need more force than usual to deprime. These I can cull as needed. I’ve also developed a rather soft hand at seating the new primers, to hopefully catch any that I’ve missed.
Hope this helps.
Doc.