Here's a quick introduction of Four Curl calls from its founder Brad Hobrock:
We all have certain "bucket list" things we want to do.  For me, making my own waterfowl calls was one of mine, and probably most serious waterfowlers as well.  Sometimes unfortunate events create the need/opportunity to act.  One of my best friends growing up, passed away unexpectedly in the spring of 2018. The first calls I turned were in memory of him.  Fast forward nearly a year and a half later, Four Curl Waterfowl was born.  The name Four Curl is based on the fact that a mature mallard drake will have four tail feather curls and the mallard limit here in the MS Flyway is four.  
The "19 Green" call is a single reed hybrid that is a mix between a traditional J Frame and a cut down.  The sound is somewhat unique in that it has a very raspy, nasally tone.  It also has tremendous range from loud hails to soft finishing ability. The name given to it, though unorthodox for a typical mallard hen call, is based on a fairly wild night at a duck camp back in 2014.  It's one of those stories, you simply had to be there to understand it! 
Four Curl is currently working on a cut down and a honker call at this time.
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