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Which book are you referring to that indicated 11 were made in 45 Colt in that serial # range?
If you have a factory letter, other than saying it's special, what cartridge does it verify as the original?
1. The factory 45 Colts were not marked with the cal or cartridge. Many 455 British contract revolvers are not marked either. See this database:
http://smith-wessonforum.com/s-w-ha...26646-455-mk-ii-revolver-research-thread.html
Go to post #223 for the latest updated database info, page 5:
2. .455 2nd Models made for the Canadians in .45 Colt:
By Feb 1916 724 were manufactured for the Canadians, chambered in 45 Colt, without a cartridge roll mark on barrel, presumed for the RCMP [H of S&W, 3rd ed., pg. 203]. All of these that are known are in the 70XXX range.
Another 15 in 45 Colt were sold commercially in 1916; likely "over run" guns from the above order. All these.45 Colts were numbered above 40XXX.
3. Your gun was serviced at the factory 10-1951. Likely a replacement 45 Colt barrel and cyl was installed and the entire gun was refinished. The 41 stamped high up on the grip frame is just an assembler/inspector stamp and of no help.
4. The recoil shield on your gun may not be shaved off at the top half of the recoil shield. The factory would have had a difficult time retaining the headspace with a shaved recoil shield just by replacing the cyl.
5. The black rings at the beginning of the chamber throats are the transitional tapered shoulders in all cyls for cartridges with a rolled crimp. The 45 ACP is the only exception and has a square cut shoulder because it has a taper crimp and must head space on the cartridge mouth. Shown here in tenntex32's 1917 45 ACP cyl:
6. You have an extremely nice 455 2nd model that went to war across the pond, made it back to the USA, converted to 45 Colt properly with a brand new factory installed cyl at the factory, and treated to a factory finish* and 45 Colt cyl.
*After WWII, the factory also polished the rebound slide stud flush because that's the way they finishing new guns after the war.