I want to do a bar musle up. And I am waiting for PI to provide me a program to be able to master that.
I have a relatively strong core. Dips and chins are still not that good though.
It's all about the false grip imo. With rings it's absolutely necessary, and even with a bar it makes the transition easier. Without it you have to roll your wrists over through the transition from pull-up to dip, and most people are gripping the bar far too hard for that (especially if the bar is a thicker one).
Here's a decent tutorial for both ring muscle-up and bar muscle-up, with good descriptions of the false grip on both:
http://www.beastskills.com/the-muscle-up/
Another really good tutorial for ring muscle-ups is here:
http://www.ringfraternity.com/tutorials/muscle-up.html
Aside from the false grip, the most important part is the ability to do full ROM in the upper part of pull-ups, and the lower part of dips... You basically want to be pulling chest/sternum to the bar, not just touching your chin over it. Make sure you're using a forward grip, and not a reverse chin-up grip, or even a neutral grip (unless on rings). With dips, you want to be dropping as deep as possible while maintaining an active shoulder.
I'd say on rings the ability to do 10 full ROM pull-ups, and 10 full ROM dips, should likely have you at a muscle up. Working up to the point of 5 sets of 10 of each in a workout is a good place to be.
On a bar... I'd increase that to 15 full ROM pull-ups, and 15 full ROM dips. Same deal with 5 sets.
If you're still having trouble with the muscle up when you hit these numbers, you can add weight to both these exercises as that will help significantly with further gains.
One caveat I will add, is that
rings will make the number of pull-ups and dips required to learn the movement far easier on your shoulder and elbow joints.