Mystery Stamps on an Antique Revolver

The revolver itself is no mystery. It's a 5" barrel S&W DA in .44 Russian that was part of a run of 2,500 blued revolvers in 1890 (mine on 10 Oct.). The head-scratcher is the stamps on the barrel. On the left side is "U.S. Armory C.T.G" and on the right side is "SMII". Normally, I see cartridge abbreviated as "ctg", no capital letters or periods. What are the odds that this is an acronym? The "SMII" may have been meant to be just "SMI", but with the "I" impinging on the leg of the "M", it MAY have been double struck. Can any of you folks point me to more reference material or a good source? I've tried every search engine and phrase I can think of and found nothing definitive.