A high quality shotgun is designed and built to not flex or expand with any reasonable load. No flex, no expansion, no wear. That's why well maintained shotguns 130-140 years old are tight as new.
They all flex. Wear can be mitiated by robust joints, low pressure, hard steel, good cleaning, and high pressure lube. But, they all will wear if used. Could a gun be worn off-face by simle cycling without firing? Wash all joints dry of lube, toss in a little grit, cycle a few hundred times, and measure. Non-firing cycling has a large movement under very low pressure. Firing has very small movement under high pressure. They will both wear the gun.
No, zero, zip, nada, mechanical joint is completely immune to wear. Good design and maintenance can make the wear small, but never eliminate it.
