I know K-frame revolvers and 125 grain jacketed bullets driven at high speed is a bad combination with the greater potential for forcing cone erosion or a cracked forcing cone ---but what about the use of cast lead 125 grain bullets??

Seems to me I read somewhere that erosion was related to bullet length, not weight. Something about the shorter lightweight bullet allowing a gap for hot gases to erode the forcing cone. Supposedly longer (thus heavier) bullets prevent much of the gas escape. If that's the case, bullet material shouldn't make much difference. If it's a lot of bull, don't blame me for beef prices.

The near-legendary forcing cone damage done to K-frame revolvers is attributed to .357 Magnum 125 grain JACKETED bullets driven to maximum velocities using slow-burning powders. I have fired many tens of thousands of 125 grain cast lead bullets with moderate loads of Bullseye, WW 231, or Unique with no ill effects on forcing cones. Pinkymingeo is correct: bullet length is what determines how much gas cutting is done when the bullet jumps the b/c gap. As it turns out, the lighter weight 110 and 125 grain bullets also have the shortest lengths. Remember the .357 Maximum cartridge? It was briefly popular until it was discovered that maximum loads tended to burn out forcing cones and barrel straps. Then it became history.