First suspicion would be head spacing.
Head space is often misunderstood.
The headspace could be perfect, but the rifle very dangerous.
The headspace could be grossly excessive, but the rifle quite safe.
If a chamber is cut too deep, but the bold face is close to the chamber, the excess headspace does not matter. For example, some guys worry about 12 thou of headspace, but they can shoot 308 in a 3006 all day long. (500 thou of headspace.)
The only measurement that matters is amount of case protruding from the chamber. This, in itself, is not headspace. I call it shallow chamber. If the gunsmith cuts the chamber too shallow, he would then cut the barrel threads to give the correct headspace, which would leave the case head unsupported.
The depth of the solid head/web varies from make to make of brass. So long as some of the solid section is supported, the problem will not be noticed. But one day, a case with a low web will be shot, and the case will burst, looking like the one above.
The barrel needs to be set back one thread; the chamber then cut deeper and the breech end trimmed. All easy to do.
Was this a home gunsmithing project? This is where I have seen this done before.
In summary, the problem is the case sticking out of the chamber and being unsupported. This is not a headspace issue.
However, if a rifle is correctly chambered (think of a Lee Enfield) and has perfect headspace, it can be made to let the case stick out by changing to a sorter bolt head. That would be the kind of excessive headspace that is dangerous.
