Those Nagent rounds press against a forcing cone surface to create a gas seal. The Nagent revolver (1895?) had a funny cylinder that backed up to rotated and then moved forward again to achieve the seal. The idea was to get more velocity by not having a barrel/cylinder gap. To me that was a little silly, as letting the bullet go slightly further forward and using more powder would accomplish the same thing with less complexity. The main real advantage to my mind is the presence of the seal should allow the shooter's weak hand to stabilize the barrel or wrap around the cylinder area without getting cut by escaping gas.
I thought a little more about Lee's friction claim. It occurred to me that with its shallow grooves, the Lee TLWC friction reduction is for the same reason bands on solid bullets reduce their friction: less bullet bearing surface is in contact with the bore. However, reducing friction is no guarantee of increased velocity. Indeed, with many rifle cartridges adding a lubricating coating to bullets actually reduces their velocity by giving up some of the resistance the powder needs to build pressure against. However, this will be more of a problem with slow powder than with fast powder. Also, because of the presence of the barrel/cylinder gap in a revolver, a revolver will see more gas vented when a bullet has more bore friction, so in that particular situation, the friction may matter more than in a sealed gun barrel. You'd have to try it and see.
The narrowed nose of a conventional bullet shape causes its center of pressure to be ahead of its center of gravity. That is, if you balanced the bullet between opposing needle points located at its center of gravity and blew on it from the side, the pointed end would catch more air than the base end and would be turned away from the air source, leaving the base facing into the wind. This is just the opposite of an arrow, for which the center of pressure is behind the center of gravity, so the feathers catch more air than the head and turn it into the wind. The exception with bullets is the hollow base wadcutter, whose center of pressure is behind its center of gravity. Some Minie ball designs may have their center of pressure and gravity co-located as does a double-ended wadcutter, so neither end favors the direction of the wind.
What that all means to bullet stability is that most bullets do not have what is called static stability in their direction of travel, like an arrow does. Without spinning fast enough for precession to correct their noses into the air stream, they will tumble. In theory, the hollow base wadcutter should be stable without spinning, but the center of pressure of such a bullet really isn't far enough behind itsr center of gravity for that be sure of stabilizing it, and I have seen them keyhole. They would also need fins to really get the air to stabilize them without spinning them.
The other factor is that when a bullet first leaves the muzzle, the gas escaping behind it accelerates to a higher velocity than the bullet has. So the bullet actually has this gas rush around it from behind and form the blast sphere you see in schlieren shadow graphs. They actually experience a tail wind from muzzle blast for the beginning of their trip and don't see a head wind until they break out of it. A hollow base wadcutter with too much powder behind it, for example, can have its skirt blown open as it exits the muzzle and be knocked off-axis before it even gets to the headwind.
The forces on the bullet in any fluid (air or water) have a lot of similarities. Indeed, Newton worked out the drag function shape coefficients by dropping shapes through water rather than air. Water cavitation eats up more energy than creating a partial vacuum behind a bullet in air does because the water goes through a high energy phase change in the process. Going through wood you run into fixed yield thresholds beyond which its resistance drops considerably. So there are differences in different media, but despite that, for short penetration and absent great deformation or turning of the bullet, they aren't so different that the ballistic coefficient still won't tell you something about relative penetration.
Incidentally, this photo of Keith's 45 Colt semi-wadcutter shows it is so close to the nose shape of a full wadcutter that it would be considerably more effective on game than a round nose.
(Attribution added to photo to fulfill Wikimedia Commons requirement.)