I believe it would have been made prior to 1950. If I can find my reference book, I might be able to narrow it down more. Those early serial numbers are not as easily traced as the later ones, beginning in 1950
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Neither of my books (James Spacek, or Tom Dance) have serial number or production info on pistols prior to 1950. The little bit of info I do have comes from Dance's book, "High Standard: A Collector's Guide to the Hamden and Hartford Target Pistols." It basically says the HD-Military and the USA HD Models were so popular, they were made in relatively large quantities for the time. They were spin-offs of the earlier D models, in that they had "exposed hammers". And, both were produced through the 1940's, even overlapping the later G model.
Just an aside, I'd use the "standard Velocity" ammo in those older models.