What period of cannon barrel do you want to simulate, or what model, meaning WWII, Civil War, or what? Naval gun barrels have gone from only a few calibers back when caronnades were used, up to 60 calibers currently. The vast majority of naval barrels were cast iron or later, steel, only a very few US Navy barrels around the time of the Civil War through the 1870's, were made in bronze. If you want some nice drawings which are fairly accurate as far as proportion, I'd look in Peterson's classic book Round Shot and Rammers.