Look the gun over again. First, check the grip frame, front and back to see if its got the factory grooving. They put them on nearly all the factory target sighted guns (but not necessarily those made before maybe the 1920s.) Its not certain, but an indicator. You also could have a fixed sight barrel stuck on a target frame. Things happen. And of course you could even get a factory letter to confirm what is suspected. And of course you can call S&W and talk to Roy and see how it came from God.

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Dick Burg