That was my thought also. I've had my share of case separations but none that close to the head.
I just carefully tried the paperclip method on those cases - tested 10-12 cases - all with the slight lines around the same area of the cases as where the separation occurred in the separated case. In each case (no pun intended) I could not detect any inside circumferential groove with the paperclip - the inside of each case at the separation area felt absolutely smooth with repeated tries. It could possibly be that such visually slight lines around the outside of the barrel of the cases toward the base could be a more sensitive test than the paperclip method. All comments are welcome.
Before everyone jumps off the cliff over full length resizing, if done properly it will not result in case head separation. This means measuring the bump with a bump gauge and caliper or the old fashion way using the rifle chambering method which admittingly is not as precise which in both instances, should result in only sizing enough so the case chambers with slight resistance i.e. .001 to .002" shoulder set back from the fire case's head space measurement.
A stripped carbide 45ACP sizing die will also size the pressure ring on '06 size cases if you can manage to push the case all the way through or at least into the die far enough.The problem with using an FL die to size case heads smaller at the web is that you also bump the shoulder. It’s the nature of the beast. You make the problem even worse by buying or grinding the shell holder so that you can size further into the base. That problem can be solved by buying what we call a ring die. It is a straight inside wall die that sizes only the base and doesn’t touch the neck shoulder area, only the base. One sells for $135.00 plus $12.00 shipping.
A stripped carbide 45ACP sizing die will also size the pressure ring on '06 size cases if you can manage to push the case all the way through or at least into the die far enough.
When I experienced CHS I felt the cause was indeed unnecessary / additional sizing at the .200 line and the CSJ .Case head separation is usually due to an improperly spec’d chamber or brass with undersized case heads. I had the same exact issue with 300 Norma Peterson brass after 3-4 firings due to the brass heads being undersized. The case over expanding in that area of the chamber then being sized back down by the FL die causes excessive working of the brass in that area which leads to creases that create separation.
Can also sometimes just be defects in the brass alloy used for a specific lot of brass.
I changed over to Lapua 300 Norma brass with proper size heads and haven’t had an issue since.
Thanks for doing that, that’s a good visual.and while i am here.... here is a donut formed after a 'few' loadings on a piece of lapua brass formed for 20p using a bushing die:
View attachment 1453270
neck is to the top. shoulder is dark at the bottom. donut is slightly ahead of the junction.