Making a duck call jig

[TomG]

The easiest way to cut that slot would be to use a key seat cutter, which would also be the shortest reach for a cutter. It would be tough to do with an end mill for the other way. My second option would be a slotting cutter, but then you would need a rather expensive arbor to hold it. Slotting, or broaching it as you say would also get it done. A boring bar tool (below) that will hold a 1/4 or 3/16 bit could be used as a manual slotter, using your quill (if your mill has one) to provide the action.

Tom