Fellas, that "shock" wave that travels back and forth in the barrel (at 15,000 to 18,000 fps depending on who's measuring it) causes smaller bore/groove diameter changes that what even the very best grade match barrels have when they're lapped to "perfection." Note that shock wave goes from the middle of the case in the chamber forward to the muzzle, then backwards to some point where it's reflected forward; that point may be the breech or back end of the receiver depending on how the barrel's fit to the receiver.
And the frequency that barrels whip at that causes the greatest muzzle axis angular movement is very low. The barrel doesn't even go through one complete whip cycle 1.1 millisecond after the primer detonates and the bullet leaves the muzzle. 1.1 milliseconds is what barrel time is for a whole bunch of rifle cartridges. And for handgun barrels, it's a whole lot shorter and if it's a revolver, how to you figure in the cylinder's effect?
Personally, I don't believe all this "shock wave" and "velocity timing" to get a given bullet to leave at some exact place in the muzzle's angle during barrel whip or diameter from shock wave expansion/contraction. Not when the same load's shot very accurate in all sorts of barrels; short skinny stiff ones as well as long thick whippy ones.