Agree. The breech shank is pretty short.EDIT
Looking closer at the pictures it looks more like an over pressure, the blow up is right at the Chamber
What cartridge, bullet, powder and load?
Agree. The breech shank is pretty short.
Either defective steel, improperly stress relieved, and/or excessive pressure at the chamber. As in fast burn rate pistol powder loaded into a rifle cartridge. Possibly a bullet lodged in the barrel just forward of the chamber.