Jim --

You might post this question on the 'Arms and Equipment' message board:

http://history-sites.com/mb/cw/cwaemb/

This caliber weapon appears on inspection reports for the Army of Tennessee during the summer of 1864.

I'm not familiar with the practice of regimental designations being imprinted on individual weapons. These were property of the Confederate government, which bought and issued them to the troops. Regulations required that a soldier being sent home on leave or to a hospital for treatment turn his weapon and any ammunition issued over to an ordnance officer. Depending on needs, these officers routinely took up some types of firearms and issued others. For these reasons I question that the '53' represents a regimental designation.