There has been MUCH written about this over the years, and much hype, confusion and outright bunk. There have been some Model 19s on which the forcing cones split, traceable to very hot 125gr. JHP loads in large numbers, some years ago. 125gr. loads at the same intensity are today loaded by Remington, Double Tap and Buffalo Bore. Shoot enough of them, and gun damage might result, or might not. There has never been any documentation of 110 gr. factory loads causing a problem, because factory 110s have traditionally been pussycat loads, compared to the 125s. It is NOT, I repeat NOT the bullet weight that matters, but rather how hot the load is that risks forcing cone damage. I.e., how much powder is loaded, and to some degree, the nature of the powder itself. Some powders literally burn hotter than others (like Green Dot), and the partially-burned residue of some powders (like AA#7)is more abrasive than in others.
It has been theorized that something about the length of the 125gr. bullets somehow causes more gas cutting and potential for forcing cone damage than longer, heavier bullets, but to my knowledge, there has never been any proof of it. Load any bullet weight up hot enough, and you will accelerate wear on the gun, whether you break anything or not.
Because they are no longer made, I still baby my K-frame magnums a bit, typically keeping them loaded with "-P" magnum loads like Speer Short Barrel or Remington Golden Saber ammo, or sometimes, full-power Speer 158gr. Gold Dots. Nonetheless, I wouldn't hesitate to shoot a few full-power 125gr. screamers through them, if need be.