Wait a sec... are we talking about rings or bar? I never did quite catch that.
Technique differs for both.
Also, like I said work powerful pullups... aim for getting the top of your abs to the bar/rings. Chin to the bar doesn't help you at all, and chest to the bar height may still be a bit lacking. If you can pull your abs to the bar then you have the ability to do one, so that's what you're aiming for.