I am are now offering jug choking for muzzle loading smoothbores of most makes and models of firearms. I cannot choke some of the models of barrels due to their chrome-lined bores. Some of those that might have chrome lined bores are newer double-barreled percussion shotguns. The chrome lining is too hard to ream and will destroy the tooling. I can jug choke 20, 16, 12 and 10 bore guns with normal steel composition. My guns are built using gun-barrel quality, high carbon steel and most modern (non-chrome) steels are fine for this procedure. I can't jug choke Damascus barrels either!
The principle of jug choking is that a section near the muzzle is reamed larger than bore size with critical angles on the front and rear areas to increase the pattern and performance of shot loads. The jug choking does not adversely affect round ball performance and in fact can improve round ball accuracy. It is not a constriction type of choke, so there is no danger of excessive pressures being developed. It is easy to clean and easy to load.