I bought some Remington .38 Super virgin, unfired cases several years back. I loaded Remington Goden Sabre bullets into them, left them on a shelf, and several months later, found that about 20% of them had cracked just sitting there. I feel it was the result of poor brass alloy, making them too brittle. The tension of the case mouth around the bullet was enough to crack them. That is what you have there, but from another maker. I contacted Remington, sent them back for examination (at my expense), and they refused to replace them in any way. I will never buy Remington brass again. I have loaded for over 40 years, and I did not contribute to the failure of those cartridges; there is nothing that I could have done to cause those cases to fail. Remington just did not want to get into an issue where they had to admit a failure and maybe recall thousands of cases or batches of bad brass.