Fatigue design:

Some items fail from fatigue (cyclic stresses). One can imagine an axle failing. What you see is a crystalline interior and a burnished exterior at the failure point. Some (pure idiots) have said that the interior part failed from "crystalization". A statement like this was an automatic "F" in college. Steel IS a crystal and that is the part that had the final failure. The initial failure were the burnished areas which gradually grew until the final broken area could no longer take the forces applied. The burnished area was crystalline but the bending of the piece allowing the two surfaces to touch each other wound up pollishing the surfaces.

Different steels and different heat treatments changes the fatigue strength of the final product. Steel can vary from about 65,000 psi strength to well over 300,000 psi. These latter steels are usually stainless with exotic heat treatments. Generally, the stronger the steel, the less fatigue life it has. Design also affects fatigue life. Sharp corners are known as "stress risers". They significantly reduce the fatigue life of the material especially if it is harder material. Now, we have LOTS of experience in picking the right steel and heat treatment and design for shotguns. A failure of a new gun by a reputable maker should be unheard of. Remember that there are numerous tests like hardness tests of basic steels. These are part of quality control/quality assurance. The steel supplier has their tests and I am sure Purdey has their tests.

Again, we are lacking information here.