About Fajing (Discharging energy)
Fa jing is a high level skill in Tai-chi that not many players can confidently say "I know HOW." So, most of us tend to sit back and see what's out there.
Almost all Tai-Chi books have a chapter on Fa-Jing. There are Long-jing, Short-jing, Cold-jing, shaking-jing, Arrow-jing, Spring-jing....and Smashing-organ-jing. To find out WHAT is Fa jing, do read those books; if you just want to "know" it, reading is enough; if you like to "understand" it, practice ten thousand rounds of form then you'll get it.
Ting(sensing), Hua(yeilding), Na(controling), Fa(discharging), are the 4 steps of Fa-jing training. If you can't sense it, you can't neutralize it; If you can't even neutralize the coming force, you can't go on to control your opponent; without controlling your opponent's center, you would have no place to discharge; if one still insist on discharging, that would be a sick intent.
Every Taichi masters will show you their versions of Fa-jing, there's no standardized method for the technique; you just have to work at it until it becomes yours.
Fa-jing is the final state of "expressing" the energy, it should not be studied along. Beginners are often interested in Fa-jing because they enjoy seeing the master flying people across the room; they can not see what's been done internally on sensing, neutralizing and controlling before the final discharging.
In every "issuing energy" postures in the form, such as Word-off, Push, and Single Whip...etc, there are transitional movements for neutralizing and storing energy, Fa jing is the final phase of the process; without sensing, neutralizing, and controlling, a player starts Fa-jing for no reason, my teacher would call it a "football tackle", not good for your cultivation.
On the 4 oz. concept, we know it is just an expression of using minimum energy, not literally to measure a 4-oz. force. In our school, we train our body to be ZERO, so when there is a 4-oz. force coming, I'd know that is a 4 oz. If one's arm has a build-in 10-oz. muscle force which he didn't know, when he applies 4 oz. to push, that would be a total of 14 oz.; same if one's body is as hard as a 40-pound rock, how could he sense a 4-oz. push crept on him? Our body should be as sensitive as a bathroom scale, only when the scale is set at ZERO can it weight precisely. And CMC style of Tai Chi is a great system to set our body to ZERO.
**** It is all in the mind, not external. I believe.