Wikipedia online encyclopedia, "Warships of the Civil War" by Silverstone, "Warships of the World" by Paine, and "Warhips and Naval Battles of the US Civil War" by Gibbons all state the Nashville had two 12-lb guns.

"Official Records of the Union and Confederate Navies in the War of the Rebellion" (available online) by Daniels states that the Nashville had 26-lb rifles.

The books by Gibbons and Daniels state that the Rattlesnake (exNashville) had six guns.