@Demi-human
See this pic from my thread on the subject:
It’s a Savage, with the ubiquitous slop between the FP and FP hole that the brand is known for. That creates the cratering which becomes a weak point.
Now, why did I get away with the first 2 CCI 400s and blank the 3rd? Likely because the thinner cup puts it on the ragged edge of failure. Not every time but once is enough. Piercing a primer is a “stop, do not pass go” event. It’s not safe to keep shooting that load until you’ve figured it out.
In my case, CCI 450s, CCI BR4s, Fed 205M and Rem 7 1/2 all perform without blanking.
Q. E. D. - Savage with firing pin slop makes craters + a high pressure round like a .223 + thin cup CCI 400 = a blanked primer
Change a variable in the above and you’re probably OK. The easiest one to fix is the primer.