I've experienced case head separation in .45-70, .30-06, .30-40 Krag, and .218 Bee. Always with handloads, always with cases that had been loaded and fired with full charges more than 3 or 4 times. Separations have occured during extraction of the fired case, but more frequently in the sizer die when resizing. Both can be a PITA to deal with.

For years now I have kept track of each batch of brass, starting with either new factory ammo or new brass. I reload with full charges only 3 times, then the brass is segregated out for use only with reduced loads.

Rifle cases get scrapped after 10 loadings.

On the other hand, I have lots of .38 Special, .45 ACP, and 9mm brass that have been loaded and fired 20 times or more with modest practice loads. Case mouth cracks, yes, but no head separations. I wouldn't try that with magnum or +P loads.