Only number that matters legally is on the Butt. I think Charlie has it right. Gun is likely stolen and stupid thief tried removing the only serial he saw. Thieves are too stupid to realize than a removed serial attracts attention much faster than a stolen serial.

If it was stolen it was long ago. May have never been reported. May no longer exist on any lists or maybe owner can't be found. If the scratched out number bothers you take it back. The 28-2 is not rare and you can find another (probably cheaper).

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