Its always difficult to talk about physical actions, because, you can never be totally sure you are talking about the same thing, however, hand to hand, face to face, you can easily convey the information.
The issue of remaining balanced and not succumbing to momentum is an interesting one.
I find a lot of westerners throw their shoulder into a punch. Throw the shoulder, drive through with the arm. The fist travels from point a to point b, however often (not always) the hips travel from point a to point a-and-a-half.
Think along the lines of fist moving from point a to b, and hips moving from point a to b. The penetration of the punch is the same, a to b, but the complete body is behind it. And if that complete body is a bit larger, so is the additional energy. Weight as a component of final issued energy.
I don’t think “coiling” works for me as a term. I understand coiling, but its just the beginning, and its a telegraph. To me, its like a cartoon cell. One frame is perfectly balanced potential energy. The next is perfectly balanced issued force. Every state contains both the balanced expended force, and the balanced potential force. It has to be a full body thing, not just a few elements. Footwork is critical, and often unnoticed or subtle. The more you can coordinate your full body, the less any single element has to carry the responsibility for delivering the power. Speed increases, relaxation under stress becomes easier.
But, internal, external? I still don’t know what that means..
I think its just an arbitrary label for something that takes lots of practice and control.
Holding the power inside your muscles, or gathering it up and injecting it into your target. Speed, focus, intent.