I agree with DARE, it sounds like a Terrier, and his estimate of a shipping date is in the ballpark. Pictures would firm that up.
In 1940 at SN 54,474 (per Dr. Jinks) production was discontinued in favor of war efforts at the factory. In June, 1949, post-war production began at SN 54,475, but there were exceptions to this for various reasons. These numbers are a good benchmark, but there are outliers.
# 63812 should likely be a five-screw Improved I-Frame, first version with the 1/2 round front sight. #66971 (in my posession) is this configuration, and it shipped 04/18/1952. My guess would be #63812 shipped in 1951 (or perhaps late 1950). Keep in mind that the production volume of Terriers was not very large,
but they were numbered within the Regulation Police serial number block.
It should look like the picture below. If not, we really need pictures.
IMG_4333.jpg
IMG_3409AB.jpg
