Tinker I suggest that 20 bore must be later than 1855. In 1820, most gun makers were still making flinters. The percussion cap was only just being invented. There were a few pill locks, then tube locks about the time the copper persussion cap came about. At that time, there were no 20 bore ctg. guns that I am aware of. There were some breechloaders, though, all the way back to match-lock days actually. Most breechloaders of 1820 + used a flint or percussion ignition system along with a paper ctg. similar or identical to the government army issue.