I'm not real familiar with head spacing. For those that might know -
Could improper head spacing have caused the casing failures? No exact count but the failures were dozens of shot rounds apart.
Conversely, could the casing blow outs cause a head spacing issue?
Reloads or factory ammo?
Most of the time I think of this it is from the working of brass over several reloads and working the brass, as it stretches the web where the brass base thins out into the thinner walls in the brass is where the brass comes from in its stretching to fit the chamber and flows forward with successive firings and you have to trim off the mouth end to keep case length in spec. You can check for this with a paperclip, straightened out with a small bend in it and insert into the case, scrape it along the interior case wall and you can feel a ring catching it if there is a problem. If you find this it is time to retire that case from loading it.
Excessive head space can speed it up to getting that ring leading to case head separation.