There are a few different factors to consider when choosing a choke tube for duck hunting. The most important factor is the type of shotgun you are using. Most shotguns for duck hunting are pump-action or semi-automatic, and each type of shotgun requires a different choke tube. Pump-action shotguns typically use screw-in choke tubes, while semi-automatic shotguns usually have built-in chokes that cannot be removed.
Another factor to consider is the shot size you will be using. Bigger shot sizes like #2 and #4 tend to work best with tighter chokes like full or modified, while smaller shot sizes like #6 and #8 can get by with more open chokes like an improved cylinder or Skeet.
Finally, you need to decide what kind of pattern you want your shotgun to shoot. Some hunters prefer a dense, tight pattern that concentrates the shot on the target, while others prefer a more open pattern with less pellet density. This is mostly a matter of personal preference, but it’s something to keep in mind when choosing a choke tube.