A friend of mine, named Howard Harlan, is well known for his custom made duck calls, and his collection of duck call/hunting memorabilia. Several years ago during a wild game dinner at Judson Baptist Church in Nashville, TN, he showed off a very similar gun from his collection, but this is the first time I have ever seen one in action.
These guns were very popular when duck hunting was a commercial business. Obviously this gun would help you take your limit.
[youtube=http://www.youtube.com/watch?v=bTQQfKxkZpk]