The serial number and format suggest this was originally a .455 Mark II British service revolver that was converted to .45 ACP (if that is actually what fully chambers). These were sometimes rollmarked "Smith & Wesson .455" on the left barrel.
The other possibility is it started out as a 1917 Army and went back to the factory for a rebuild, including restamping the butt with a commercial format serial number and possibly a nickel refinish. Some work occurred in October 1947.
The barrel really appears to be 5"; the original would have been 5.5" and someone took the 0.5" off.
The 3615 on the yoke and frame cutout shows the parts were original from the factory. The 1/8" comment still needs a reply
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