Its possibly a correct number. Or lets say that back in 1948 they made a gun with that serial. You question it like you're not sure you read it correctly. Without seeing the gun or a picture, I have no way of knowing if you read it right or not. There are other places on the gun where its easy to see the number. Open the cylinder and look on the rear face, like where the cartridges go in. It'll be smaller, but often easier to read. Then while the cylinder is still swung out, look at the flat on the underside of the barrel. Use a magnifying glass. All the numbers should be the same.

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Dick Burg