MG,
Here's your answer....not real British guns.
Her first 20th century restoration in 1906-1907 saw fifty-five replica guns made for the ship. All of the present guns were cast for the 1927-1931 restoration with the exception of two 1812-era replica carronades on the after quarter deck. Cast in 1981, these carronades are closer to Constitution‘s 1812 spar deck armament. The gun deck guns were cast in the Charlestown Navy Yard in 1929. The pattern of these guns was based on a British siege gun that was abandoned in Boston during the American Revolution and is currently displayed near Harvard University. The decision to cast “British” guns was made by Lieutenant John A. Lord, Supervisor of the 1927-1931 restoration. He based his decision upon inaccurate research that led the Navy to mistakenly believe that Constitution was outfitted with British guns in 1812.
https://ussconstitutionmuseum.org/20...dern-armament/