ORIGINAL: quiksilver
If you can master the purr, you can move on to the fighting purr, which is much more aggressive with clucks and putts interspersed in the sequence. After that, you can start to master the gobble, which is darn near impossible.
See I am the other way around. I thought the gobble was a snap. Purring, by using what call makers refer to as the "gargling" method is seemingly out of reach for me. Too many years of calling ducks I suppose...too many bad habits. I keep hoping that eventually I'll do it by accident horsing around with one...but we'll see.
The way I purr is using the motor boat method. For a fighting purr, I use the normal side of the call, short reeds down. For a hen purr, I invert the call, which gives it a much higher pitch. I stretch my mouth out, so I don't get to much "motor boat" noise. Works for me and mine.