I've seen various shapes of rimbases such as square ones before, also half-rimbases (French), so round isn't the only way they come. I'm sure the gun was finished. I'm thinking the lack of markings meant it was made for sale to militias or whomever wanted them rather than governments. The markings are there mostly because of government regulations. Often makers put their marks on their products anyway for advertising etc., but I have seen many nice unmarked cannons, both iron and bronze.