Not necessarily . I have see at least two guns blow with factory shells in them. One was a BT-99 in Ok. years ago. The other was a 20 ga. 1100 Skeet gun with factory skeet loads( I knew the guy personally). I never did know what happened with the BT but the guy with the blown up Remington settled quick, when he sent the gun ,shell, and witness statements to Remington and gave him a brand new 3200 4 barrel set. He signed a settlement statement and that was that. You are correct that metal fatigue is irreversible and the fact is there is always a possibility for flaw in the metal at casting. There is also the possibility of flawed factory produced ammo. Nothing is perfect or fool proof.If you shoot factory ammo, you will never have a problem. This type of thing happens when Trap shooters try and get a bit more oomph out of their reloads by using powders designed for .410's. Metal fatigue is irreversible and, eventually, BOOOOM!!!