Hello Doyle:
Both Jim and Art are correct as the gun referred to was a 30 pounder Parrott Rifle with a bore diameter of 4.2", Model M-1861. It is reported to have weighted 4,190 pounds. The book "The Big Guns" by Edwin Olmstead, Wayne Stark, Spencer Tucker, 1997 ISBN #0-88855-012-X) clearly identifies this gun on page 114 as "Long Tom". It was built in June 1861 and was in the initial batch of production for this rifle type. Unfortunately, this gun does not exist today but the most similiar example of this gun survives at Fort Pulaski GA, in an deteriorated condition. Three examples of the next production are in Hennepin IL Cleveland OH and Vicksburg National Military Park in a better condition, if you would to see an example. Hope this helps

Ron