I had an early Model 29, 6" barrel. Heavy usage with magnum cartridges resulted in sheared off pivot pins, both the trigger pin and, I think, the pivot pin for the locking bolt, or maybe it was the hammer. After several repairs, S&W told me they were getting new machinery to install these pins, as the pins were re-designed to eliminate stress points. They kept my gun nearly ten months to install the "endurance package" but when I got it back, no more troubles.
I sort of kept a log of that gun (as I do for all my revolvers) and up until that work was done, it was the most often in need of repairs of any of my revolvers. No longer have that revolver, but after the work was done, no further problems were encountered.
Those pins were a press fit into the frame, and sheared off under recoil.
Bob Wright