Arent case head separations normally closer to the base?
Case
head separations are just above the solid head of the case. Always. That's what makes them a
head separation.
Anywhere else and they are just case separations, the OP called it correctly.
I have seen brass separate that way before, but its ultra rare in civilian firearms using modern ammunition. Rare, not impossible.
I put a single instance down to defective brass. IF it were due to reloading practices and case/rifle fit it would show up (eventually) on other cases and eventually the entire lot. (and it is normally head separation when that happens, due to case stretch thinning the case)
It's possible it was bad anneal leaving the case too brittle to stand multiple firing cycles and it happened to fail across the case body because of that. I can't say for sure, but that might be possible. Again, it would be an uber rare event.
Back in the 70s when I was there, the machine gunner's "support kit" included a broken shell extractor. But machine guns are a
slightly different situation...
Still, getting one and having it in your toolkit "just in case" doesn't cost much or take up much space. It's one of those special tools you'll probably never need, but if you do, having one can save you work and possibly $.
As the OP found out, an oversize brush often works, BUT you can't, and shouldn't count on it.
A tap (or a screw) of just the right size can also work. BUT, you need to be VERY CAREFUL seleciting a tap of exactly the right size and NO LARGER. You need to choose one large enough to get a good "bite" into the brass, but not so wide it will cut through the brass and cut into the chamber steel, that would be a BAD thing.
When a case breaks in half in the rifle chamber (like yours did) the front part is stuck, but its usually not stuck HARD the way a case stuck in a resizing die is. SO an oversize brush, or anything with a hook the right size will usually pull the broken front part out.
USUALLY...