Many, I believe MOST carronades had a loop cast under the barrel that mounted on a bar on the carriage as this on the Constellation in Baltimore.
The author of the book Artillery and Ammunition in the Civil War (Warren Ripley)states this to be a fact.
One problem with the carronade was the barrel center of gravity changes as the gun rotates causing a nose down condition after fireing.
This condition happoned on all below center trunnion pieces.
This is one reason for the loop cast on the barrel.
I don't believe the Hern barrel is a true Carronade.
If I am wrong in this belief, please correct me.
Kap