You fellas should check out this page from Varmint Al's website:
[color:#000099]Link to Esten's tuner[/color] At the top of that page is an animation showing the barrel deformation as the bullet travels down the bore, based on FEA models. The barrel deforms, or bends, but Al states that the oscillations that you dudes are discussing do not occur until AFTER the bullet leaves the muzzle. See quote below, from the link above.
The can/silencer/suppressor acts as a mass damper during the oscillations and changes the deformation of the barrel. If POI is lower with the can/silencer/suppressor, then it makes sense since the muzzle would not project as high.
CONCLUSION.... Maybe the "consensus" was that a rifle barrel vibrated in one or more of the mode shapes when fired. That was because the mode shapes and frequencies were easy to calculate and they did seem to answer some of the questions. From these FEA dynamic pressure calculations, it appears that the recoil and forced deformations are much more important than the natural vibration modes in determining where a barrel is pointing when the bullet exits the muzzle. Then after the bullet exits the muzzle, the rifle barrel vibrates in its various natural frequencies and mode shapes. Put another way, consider a guitar string being plucked. One pulls the string into a position (forced position) then releases it and the string vibrates at is natural frequency. The recoil and bullet motions "pulls" the rifle barrel to a new shape and once the bullet leaves the barrel, then the barrel vibrates. However, the addition of the scope to the model has shown some small high frequency vibrations superimposed on the forced deformations, both of which, slightly alter where the muzzle points before the bullet exits. For lowering the amplitude of the high frequency vibrations, it appears that even an "out of tune" tuner is better than no tuner at all.
