Unless I am mistaken the S&W revolvers built for .45Colt have a longer cylinder than those built for the shorter .455Webley. If that is truly the case then I would not expect to see as much of a gap between the front cylinder face and frame nor would I expect to see so much of the barrel breech showing through the frame if this revolver truly started out life as a .45Colt.

Someone please correct me if I am wrong but this does look to be an anomaly with the OP's example if he is thinking it was originally chambered in .45Colt.

It was not uncommon to convert .455Webley caliber examples to .45Colt or .45acp before being sold onto the U.S. market..........much like the many .38S&W caliber U.K. Victory revolvers that were converted to .38special before being sold onto the U.S. market.