Would not the shock wave and harmonics you refer to be initiated from the barrel group when the ball hits the forcing cone and is trying to separate from the arbor? What then would it matter wither or not it transfers this energy back through the arbor end? What matters at firing when the barrel group is trying to tear off the end of the arbor and move down range is that all the pressure points that are stopping this are equally loaded on both sides of the barrel slots and under lug. These three points are what align and determine the bore axis movement and where the projectile will print on target. At firing when all the seat points are loaded and the barrel group is in tension is when harmonics are at peak. These are concentrated in the barrel not the frame which the arbor is anchored to and a part of.
We've established ( in my mind any way) that the arbor end contact into the hole end plays no part in arresting arbor tip separation and that harmonics in a short barrel gun with several joints in it's construction is probably not effecting accuracy in a substantial way, now were trying to understand what if any part vibration or shock wave harmonics have in gun longevity, with or without arbor end contact.
My thinking is if the key fits properly in all slot seats and is adequately hard, then barrel lever loading of the ball is removing any potential joint movement slack that could batter the gun loose. Stand loading the cylinder would negate this if wedge fit is sloppy. but then a sloppy fit or soft wedge will cause battering even if arbor end fit were snug.
These are the reasons I maintain that arbor end fit into the arbor well of the barrel is relatively unimportant to both accuracy or longevity and that Pietta probabaly understood this as well . Before CNC driven equipment was installed arbor end fit would have been hand fitting which would have increased the customer cost. Switching to CNC driven equipment is the probable reason for the tightening of this and all other tolerances in newer models to compete better with Uberti , which is a good thing.
Again, one mans thoughts an opinion. A very interesting discussion and exchange of ideas !
Below is my synopsis of what you have described just to make sure I am interpreting everything the same way you are.
Basically, as the ball enters the barrel and transfers force forward, the barrel begins to pull forward on the arbor by way of the wedge. When that happens, the wedge pushes the forward end of the arbor, which creates the force which could break the arbor as shown in your pictures.
The question as to whether an arbor being seated against the base of the arbor hole can keep it from breaking will hinge on the relative properties of the materials involved.
If the material in the arbor achieves a breaking point after being stretched a certain amount over a certain number of rounds fired, then having the arbor seated against the base of the arbor hole could keep that arbor from breaking if the material the barrel lug is made of keeps the arbor from stretching to that point at which microscopic fissures begin to form. Under those circumstances, the arbor will be unable to stretch enough for those fissures to occur.
If, however, the barrel lug flexes enough to allow the arbor to stretch to that breaking point, then having the arbor seated against the base of the arbor hole may not help prolong the life of the arbor because the lug will move forward far enough that it won't support the end of the arbor when the weapon is fired.
Ultimately, a strong arbor is the most important requirement if the strength of the barrel lug varies significantly from one weapon to another, moreso than having the arbor seat against the base of the arbor hole.
I will, however, stand by the idea that having the arbor seat against the base of the arbor hole keeps the barrel from snapping back against the wedge excessively after the bullet exits the muzzle. This is where the benefit of a fully seated arbor seems to best come about.
Only a metallurgical analysis can answer the aforementioned question, and that analysis would only apply to a given revolver or specific run of revolvers where manufacturing standards are very specific.
