My guess is that the auction house was using the assembly number as the serial number. Happens all the time by folks not familiar with S&W serial number locations. The HP was produced starting 1954 and had an "S" prefix serial number. Became the model 28 around 1957 when the government required all firearms to have a model number. The 28-2 (second engineering change) happened around 1961 with the change of the cylinder stop and the subsequent elimination of the screw in the trigger guard. Diamond stocks went away in 1968 and "N" prefix serial numbers started the next year in 1969. The 28-3 (third engineering change) happened in 1982 and eliminated the pinned barrel and recessed chambers. Model 28 was discontinued in 1986.

PS: In looking at the photos again, the first gun with the wood stocks does not appear to have a satin finish like a HP should. The second photo (I believe that the hang tag says E2) does appear to have a dull satin finish and is wearing rubbers.

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James Redfield
LM #497