GLS,
In the book, The Image of War, Volume 1, Shadows of the Storm, pages 116, 117 and 416 are pictures of perhaps that very barrel along with another of the same pattern, mounted on fine looking, very well made wooden flask type beds with small front trucks (wheels). The pictures are of the Confederate Trapier Mortar Battery on Morris Island from which they bombarded Fort Sumter at the start of the Civil War. The book states that these pictures may be the most important confederate pictures on the entire war from a photographic standpoint and the fact that they may be the first pictures made of the war. These pictures were discovered in recent years and are probably copyrighted and not in the public domain. There is a drawing of one these pictures on page 63 of the book, Artillery and Ammunition of the Civil War, by Warren Ripley.
Information from the other posts indicates that the mortar in your pictures was excavated in 1959 at the fort and was also a trophy gun. It had to be one or the other, but not both, unless the Union Army was still capturing Confederate guns as late as 1959.
Max