As an addendum to Mr. McGhee's post.

Artillery captures from the Mexican-American War probably provided the metal poor South with much needed material. I make this assertion by noting the lack of trophies from that war in areas controlled by the Confederacy.
St. Augustine, Florida contains several examples of artillery from the Mexican-American conflict of 1848 and earlier. The Castillo De San Marcos, a National Historic Site, is well worth the visit should the topic of this forum pique your interest. As you exit the main body of the fort to the gun paraphets you will notice a metal door. Please ask the guide what was in there.

Regards, Hank