After the first bombardment, at least thirty minutes had to pass before reloading. When the gunpowder exploded, tremendous heat would scorch the cannon, and the rings' role was to keep the bronze cannon from swelling and bursting.
So that was the purpose of those rings. The reason for making the cannons out of expensive copper rather than using cast iron was simple. Cast iron explodes easily, while copper endures well.
So one of the artillerymen's most important duties was the painstaking work of fanning the heat-scorched cannon or covering it with a water-soaked cloth to cool it quickly.
Of course, keeping water out of the fuse fitting area was extremely important. If someone failed to do this properly, Schneider would come charging over and send that artilleryman flying with a kick.
