Here are my assembled models, painted and gloss varnished before final matt coat on carriages.
The TA Miniatures pieces are excellent. Featured here is the 8" Columbiad on casemate carriage. These are big guns. The surface area is 6" x 4 " and the curved rail in 2 sections is 6" along the curve.
TA also makes a very small Mountain Gun, shown here for comparison. It is also a great model.
The next gun on a naval carriage is a Crimean War Russian 36 pdr by Great War Miniatures. It is the best gun I could find in 28mm scale to represent an ACW 32 pdr broadside cannon. It is also a fine model, available from North Star Figures. Foundry also makes a 32 pdr British gun but I have not seen it up close.