While we're at it, properly designed and fabricated shotgun barrels, manufactured with the appropriate steel do NOT undergo low cycle fatigue; elastic deformation when the yield strength is exceeded.

This obviously is not a shotgun barrel but demonstrates the "waves in the sand" fatigue striations



150X SEM with fatigue striations transitioning to "fisheye" elastic deformation (stretching) then to cleavage



As said, I only play a metallurgist on DoubleGun and for additional light reading:
http://www.martin-moeser.de/Images/Fractography.html
https://www.efatigue.com/training/Chapter_3.pdf

https://sites.google.com/a/damascusknowledge.com/www/home