well i use a tube call so I pretty much have the gobble down on that one (took me a few years to get it close and still has some work left) but I have been trying to get a gobble on a mouth call for some time. found the vid below that makes it as easy as i have tried. It uses the same basic technique as a tube call so those that already use a tube this should come somewhat easy. Anyways just thought i would share. I pretty much got it working after about 30mins or so once I got comfortable on how to hold it on my lip without spitting it out on the "ticka - ticka" part
http://www.youtube.com/watch?v=Kk8DwxMzCVk
http://www.youtube.com/watch?v=Kk8DwxMzCVk