This issue has little to do with the use of H110/W296 in handloads utilizing bullets weighing less than 140 grains. It has to do with the intended use of the gun envisioned by Smith & Wesson when designed, the popularity of the gun in the LE market along with the surge in popularity of the then new SuperVel type light HP bullet ultra high velocity ammo.

The design concept for the Model 19/66 was to build a medium frame LE duty .357 magnum revolver with target options which would utilize .38 Special ammo for practice and magnum ammo for qualification and duty carry. Their design was fine for this type of application but then the light bullet high velocity revolution happened and widespread problem began to appear. Smith & Wesson issued the recommendation not to use full power ammunition with bullets lighter than 140 grains as a response to the issues. It was reaction to the issues experienced by LE agencies equipped with S&W k-frame .357 magnum revolvers which at the time dominated that market. Obviously, these revolvers were loaded with factory ammo and not reloads.

Gas cutting of the top strap isn't a problem but forcing cone erosion & cracking is the issue along with fracturing of the frame's barrel mounting boss. To this day it is not unusual to find original k-frame .357 revolvers which exhibit eroded or cracked forcing cones and cracked frames in the used gun marketplace and no factory new replacement barrels exist.

Bruce