I would think that evidence OSR would be most apparent in a vintage drilling IMO due to the usually thin barrel wall thickness and the abundance of soldered surfaces on the rifle barrel - especially if of the double shot barrel over the rifle barrel configuration.
California, being at the forefront of the lead ban, and where there is still a fair amount of boar and deer hunting being done will probably be the most likely place for these problems to originate (if we assume OSR is from monos and hunters will be required to use such bullets).
Taking into consideration that many combos are in a 9.3mm chambering, I bet there are more than a few shooting Barnes' (or another maker) monos right now.

Also, I am confused as to how a "egg in the snake" bulge can occur any further down the barrel than at the point at which the bullet is "swaged" to the land and groove dameters.
IMO, unless the bore is tapered, the bullet is sized to the rifling immediately after leaving the chamber. If not, then monos fired from a 24" barrel would be expected to be of a smaller diameter than if fired from a four inch barrel - which I suggest is not the case.