The statement about what happens when the bullet does not move is correct, but it has no bearing on this discussion, and nothing I have said contradicts it.
It is certainly true that recoil is a force applied in a direction parallel to the barrel and opposite to the direction of travel of the bullet, but if the quoted statement is meant to somehow imply that recoil is imparted magically to the entire gun, that is clearly incorrect.
The recoil force is applied to the breechface, and if the breechface can move independently of the rest of the gun, then it will do so. That is exactly the principle that recoil operated firearms operate on. If the recoil force were not applied to the breechface, recoil operated pistols would not function. Since they do, there is really no room for debate on that issue.
Recoil is a force applied in the opposite direction of the bullet travel as a consequence of the bullet moving forward. It is reasonable to state that recoil force is applied to the breechface although some of it is potentially applied to the barrel via the friction of the casing against the chamber walls.
In an autopistol, the recoil force results in the slide and barrel moving to the rear—opposite the direction of bullet travel. The slide moves because the recoil force was applied to the breechface and the barrel moves primarily because it is locked to the slide initially.
If recoil force were somehow imparted to the entire gun, then there would be nothing pushing the slide back separately from the frame and an recoil-operated autopistol would not cycle.
It is impossible to understand what’s happening without understanding that muzzle rise is NOT recoil. Muzzle rise is an EFFECT of recoil under certain circumstances.
In the first sentence, everything stated about recoil is true. HOWEVER, then, the second sentence continues as if recoil is still the topic, but in reality the topic has changed to muzzle rise. Recoil, in and of itself does not necessitate any sight compensation. Muzzle rise is not the same as recoil and if muzzle rise occurs while the bullet is still in the barrel then the sights will have to be set to compensate for it. Muzzle rise only occurs when the restraining force on the gun is below the point on the gun at which the recoil force is applied. As a consequence, if no significant restraining force is applied, or if the restraining force is applied at a point directly behind the point on the gun where the recoil foce is applied (as opposed to below it), there is no significant muzzle rise.
That is exactly the situation immediately after an autopistol is fired. There is no significant restraining force applied to the slide motion so it moves straight backwards INDEPENDENTLY OF THE FRAME until it meets significant resistance.
Muzzle flip (not recoil) in an autopistol IS caused by the barrel/slide being stopped by the frame and that is why muzzle flip has no significant effect on the bullet which is long gone by the time the slide stops.
That’s exactly what the diagrams show—they show that muzzle rise does NOT have any significant effect on the bullet in the autopistols because it IS long gone by the time the muzzle flips. That is because the muzzle doesn't flip until the slide/barrel hit the frame and the restraint of the shooter's hand causes the gun to torque upwards.
If muzzle rise did occur while the bullet was still in the bore, the boreline/sightline would show the same kind of compensation as is seen in the revolver. It would HAVE to.
No, the drawings are not puzzling at all, they simply demonstrate that autopistols are different from revolvers. The diagrams are the evidence that explanation provided is correct.
The important concept is that recoil ONLY causes the muzzle to rise when the resistance to the recoil force causes the gun to torque upwards. Operating as if muzzle rise and recoil are inseparable or identical will make it impossible to understand the diagrams. Muzzle rise and recoil are not inseparable. For example, if there were just a slide/barrel floating in space and the cartridge was fired, the slide and barrel would move straight backwards. There would be no muzzle rise because there is nothing to cause the muzzle to torque upwards.
For the brief moment before the slide/barrel hits the frame, the space thought experiment is a great analogy for what happens when an autopistol is fired. When an autopistol is fired, there is initially nothing causing the muzzle to torque upwards because the slide and barrel can freely move straight backwards. So the muzzle doesn’t flip--the slide initially moves straight backwards with no significant muzzle flip because there is effectively nothing restraining the slide from moving in the direction that the recoil force is being applied or trying to change the direction.
Recoil instantly causes the muzzle to rise in the revolver because the entire revolver (frame/barrel/grip) is essentially one piece when assembled and therefore can only move as one piece. As soon as recoil begins to move the revolver, muzzle rise also begins. That is because the shooter’s hand immediately resists that motion and resists it at a point lower on the gun than the point at which the recoil force is applied. So recoil movement and muzzle rise in a revolver both begin at the same time, at the instant that the bullet begins to move. The recoil force is immediately restrained in such a way as to cause an upward torque and that means that the muzzle rise begins immediately.
Autopistols are DIFFERENT from revolvers. Of course, the recoil also begins instantly upon the bullet moving in an autopistol, as it must. The recoil force is applied to the breechface of the autopistol exactly as it is to the revolver, but that’s where the similarity ends. The huge difference between the revolver and the autopistol is that the barrel and breechface can initially can MOVE independently of the frame in an autopistol. So unlike the revolver where the restraint of the frame immediately causes muzzle rise, in an autopistol, the restraint of the frame by the shooter initially has no effect at all. Initially, there is no effective resistance to the recoil motion because the slide/barrel can move independently of the frame and that means that the slide/barrel move STRAIGHT BACK in recoil—in the direction the recoil force is applied.
The muzzle does not rise in an autopistol until something tries to change that straight back motion and that doesn’t happen until the slide/barrel motion is arrested by the frame and the restraint from the shooter's hand comes into play.
Since that happens long after the bullet is out of the bore, the muzzle rise in an autopistol doesn’t affect the bullet.
What the diagrams show is that the muzzle of a locked breech autopistol doesn’t really move appreciably in the vertical plane while the bullet is in the barrel. Said a different way, what the diagrams show is that although we know that the slide clearly begins to recoil immediately, recoil in an autopistol does not result in muzzle rise until after the bullet is out of the bore.
Again, any confusion stems from viewing this problem as if muzzle rise is inseparable from recoil. It is not, and that is where the disconnect is occurring.
Without understanding that muzzle rise is not the same thing as recoil, it is impossible to grasp what the diagrams show is happening when an autopistol is fired. Muzzle rise is a POSSIBLE consequence of recoil, but it is not the same thing as recoil. One can’t say “muzzle rise” when “recoil” is the proper term and always have the statement involved remain accurate. One can’t say “recoil” when “muzzle rise” is the correct term without sometimes creating an inaccuracy. Recoil and muzzle rise are related in that recoil causes muzzle rise in some cases, but they are not the same thing and the terms can not be used interchangeably.
The reason that the autopistol bores are angled slightly upward is to create the ballistic trajectory necessary if the bullet is ever to impact in alignment with the sights. It isn’t because the muzzle moves down in recoil. Since the bore is below the sights, the bore must be angled slightly upward to get the bullet up to the line of the sights.