Bob,
Information about this gun, the Hughes Gun, is very sketchy and in bits and pieces. On-line search lists a arsenal called Brandon Arsenal and other locations but could not get info from these locations. I did get information that states up to 50 guns are believed to have been manufactured at the Street & Hungerford Company in Memphis TN in October 1861. They were built under the patents owned by D W Hughes. The article said only one gun survives today but further reading implies another Hughes Gun is in a collection. Some work on the Hughes guns was done at Jackson MS. The material of the gun is bronze and some wrought iron used probably in the under carriage.

The gun is a 1.5" smoothbore gun that fired a one pound lead ball up to 3 miles. It had a fast rate of fire being fired 6 to 8 times in one minute. A percussion cap provided the spark for the firing. The barrel was 47.5" and the breech section was 19" long. The bore was 1.5". It had a water jacket over the barrel to cool the barrel during firing. The gun weighted 80 pounds This gun was used in the fighting at Island #10 in early 1862, used by the Pointe Coupee Artillery of Louisiana. The battery was commanded by Captain Richard A Stewart. The Hughes gun was little used after Island #10 probably because the projectile was too small.

There is a reproduction of the 1.5" Hughes gun offered for sale on-line for $64,950, price just reduced from $89,000.

Most of this information came from on-line subject search so you may continue as I left some info for your curiosity. Check for some manufacturer being at Pinola MS.

Hope this helps
Ron