I thought it had less to do with gas, copper jackets, or anything else than the energy of the bullet with it hits the forcing cone. the hot 1,400 fps and up 125's hit those forcing cones with a whole lot more energy that the 158's that the gun was designed around. All the horror stories I have read on this subject didn't seem to start big time until the 125 screamer's started going into use. It seems counter intuitive at first that a heavy bullet would hit softer than a lighter bullet but it's all about how much energy bleeds off into the forcing cone. I'm sure if you were to load up a 158 up to the same velocity as the 125 screamer's then you would get the same troubles. But I still look at a different way. If S&W has decided they don't want to make any more K frame magnum barrels then why would I be in a hurry to wear mine out? So the max 125 I would use is a Golden Saber or similar FPS load or a nice mild to medium 158 or I just shoot all the .38 special that I want.