From an article in the South Carolina Historical Magazine from April, 1996 by C.R. Horres Jr., the following information was obtained:
Originally 15" Columbiads (50,000 pounds ) were desired, but these proved to be impossible to be cast by Southern foundries. Captain Alexander Theophilis Blakely persuaded Major Caleb Huse to allow him to cast two experimental 12.75 inch rifled guns with carriages and 100 rounds of ammunition for the cost of $600,000 Confederate dollars. When finished the guns weighed nearly 50,000 pounds each and the carriages with all accessories weighed 58,000 pounds. The finished guns were 16 feet long from muzzle to breech and they were cast by the George Forester and Company's Vauxhall Foundry. Due to the massive size and weight of these guns, they proved difficult to transport. They were finally transported on the former Confederate raider Sumter along with 150 solid shot 20" long weighing 650 pounds each and 50 shells 22" long weighing 470 pounds each. The guns had to be shipped standing up which left the Sumter appearing to have three funnels. The existance of these guns was already known to the Union and orders were given for them to be captured before arrival. These efforts failed and they arrived in Wilmington on August 18, 1863. Due to the size and weight of the guns, special railroad cars had to be constructed to get the guns to Charleston and the first gun arrived on August 25th. The guns were to be emplaced on the Battery in Charleston and a temporary railroad track had to be laid to get them there. However, once the first gun had been transported to the Battery, it was decided to emplace the second gun at Frazier's Wharf. During one of the early test firings, due to improper loading, the cast iron breech of the gun on the Battery cracked in 11 places which required a cast iron plate to be bolted around the cracked breech. Union forces were aware of the guns' locations and close observations were made when they were test fired (they were never fired in anger). The only records of the gun's performance was from an October test firing which reported that a 470 pound shell could reach 6600 feet at 2 degrees elevation, so whether or not they had a 5 to 7 mile range was never proven. Also, they were shown to be not very accurate as the bolts tended to tumble end over end and coupled with the failure of the first gun during testing; these factors cast great doubt on the value of these weapons, except for a psychological value. The guns were destroyed on February 17, 1865 and the only portions of the guns existing today is the damaged breech in the Washington Navy Yard and a 500 pound fragment that was blown into an neighboring attic where it remains today. Thirty of the bolts were used to outline a Revolutionary War fortification on Marion Square, but they were sold for scrap in 1883-they brought $50.00.