fwiw, there's more than one kind of ja jing. it depends on the effect you're after. chen guys use a lot more long, striking type fajin and say, southern mantis, uses more short fa jing, which is often used for say, snapping a wrist. in order to do that you need to lock the opponents structure, which when applied more gently can result in a bouncing out type of effect on a training partner, but it's not the point necessarily.
So how do they work? What's the differences between the two?
I was just in Tempe for a meeting. I forgot you were there.