The ordnance departments of the confederate army and navy inherited the gun sizes and standardizations from the existing technology of the federal military services. The manuals, specifications, research, development and training were all from the federal government. The confederates were too busy establishing their military services and foundries for production of guns, to orginate any new technologies or new types of guns. They captured many guns from the federals in the coastal forts they seized at the start of the war but these were of the existing older types. The confederates did rifle some of the large guns and began production of rifled field guns. The Brooke rifle, designed by John Mercer Brooke, was an improvement of sorts and were of confederate origin. The ammunition used for these guns also contributed to the success of the Brooke rifle. The 6.4" and the 7" brooke cannon which were the early production models of the Brooke and all were rifled. Later in the war, Brooke built the 10" and 11" models but since they were all smoothbores, little new was contributed. The 8" was built mostly as a smoothbore but a few rifles were built. The 8" had limited success. The confederate lacked the ability to forge any cannon larger than 11" as none larger was made while the federals forged guns as large as the 20" Dahlgren. In summary, the rebel information came from Uncle Sam and they couldn't match the lager federal guns.
Regards
Ron