[tobnpr]

Could definitely be a headspace issue.
Those case splits aren't at the case necks- they're at the shoulder, and extending down towards the case head.

Is this something "new", just now- with a different batch of ammo?

If so, probably bad ammo. You need to try some other ammo. If it happens with other ammunition, you might have a chamber problem...

Split cases mean the case isn't sealing against the chamber wall- and you're losing combustion gases. Could be the ammo- could be a potentially dangerous rifle. You need to find out which.