This is the craziest thing you've ever heard!!!
But if you want to make perfect and I mean "PERFECT" hollow pop clucks???
Get yourself a children's cork pop gun,,I mean literally a kids toy,,the kind of kids toy gun that has a cork you put into the end of the barrel and its connected by a string.
When you pull the trigger and it's forced out of the barrel it sounds amazingly like a real hen turkey cluck and I mean dead on accurate. I even thought of entering a calling contest in the cluck division if they had one.
If you think I'm crazy give it a try it will amaze you the first time you hear it and make the connection.