Maybe I'm missing something, but how does the twist push new lead out if it has a limited range of motion? Or do you twist open, let the lead fall out to the desired length, and then close it back up?
Mechanical pencils work by passing the lead through a collet.
When pressing the plunger down, the collet draws the lead out for a short distance before the collet releases the lead. At this point when the collet is released, the lead has been extended a short distance. With the collet released, in most mechanisms, the internal friction is enough to overcome gravity, thus preventing the lead from just falling out. However at this point the lead can be manually pulled out farther or can be pushed back in because it has been released by the collet.
Releasing the plunger, the collet starts to retract (while it is still not gripping the lead) until it (the collet) is once again compressed causing it to grip the lead. In this "normal" position, the collet is closed down on the lead allowing writing pressure to keep from pushing it back in.
Twisting the transmission one direction provides the same internal motion as pressing a plunger (click mechanism) down and holding it down. Likewise, twisting the transmission back to it's "non-extended" position provides the same internal motion as releasing the plunger (click mechanism) to allow it to come back up. I assume the same internal motion occurs when the bolt of a bolt action pen is pressed down and then returned back up.
Dave