When the 19 first came out, the superior steel and heat treat was a fact...but, 10-15yrs later, such better steel and heat treat may have been done across the board, such is technological and manufacturing change. It still leaves most .38Spl cylinders too short for anything but lighter bullets in magnum brass, while seating the heavier bullets maybe the required hair deeper with magnum loads could raise pressure enough to test that steel and heat treat hypothesis. I try not to play too much past known things when holding explosives. A different matter in larger diameter and thicker walled cylinders of N-frame or Ruger diameter. Would not want to take much chance in even an L-frame cylinder, which is smaller diameter than even the old model Blackhawk .357 cylinder, which could be bored out to .44Spl while the L-frame was only large enough for a 5-shooter in same caliber. I think the J-frame cylinder (not frame) is even stronger than the K-frame, it thicker walled and locking notches offset from thinnest point, unlike the K-frame. The notches are where cylinders intially bulge and then blow.
