O.K., lets try one more time.
The barrel threads on a .38/.357 K-Frame measures .542" O.D., not counting the gas-shield ring relief cut on the bottom of the barrel shank.
The barrel shank on an N-Frame measures .668", and it doesn't have a relief cut in the barrel shank weakening it.
By the time you cut the forcing cone in a .45 caliber K-Frame barrel, it would almost be a knife edge at the gas ring relief cut.
Further, the cylinder wall thickness on a .38/.357 K-Frame is about .083".
A .45 ACP case measures .476" at the head.
Subtract the .380" of the .38/.357 chamber from .476" and you have .096".
Divide that by two, and you have only .049" cylinder wall left, or only about half as much as on a .38 Special.
And you have seriously cut into the cylinder ratchet / extractor star on the other side of each chamber, which would make timing very difficult.
Bottom line = K-Frames are not big enough to chamber them in .45 ACP and have any safety margin or timing reliability left.
rcmodel