I'll throw $200 into the pot for a test. In a few months I might be able to get around to doing something similar myself(with a bolt action I plan to rebarrel, not a double!). If I do I'll share the results here.

I think two points can't be emphasized enough.

The first is that chamber or peak pressure has nothing to do with the issue. It is a matter of barrel thickness/strength vs bullet hardness. This should be obvious when you consider that peak pressure usually occurs when the bullet is only 8-9 inches from the chamber and drops rapidly thereafter, yet OSR occurs at the low pressure/thin muzzle end, not the high pressure/thick end. I've never heard of it just in front of the chambers.

Secondly, the human eye is incredibly good at seeing flaws that are difficult to measure or photograph. Take a seemingly perfect polished metal cylinder and sight along it at a low angle and look at the reflection of a light on its surface as it is rotated. Any flaws will be obvious, but I'd have an extremely difficult time photographing it or measuring it with a runout gauge. As Wright mentioned a simlar technique is used when you inspect shotgun bores. For a flat metal surface, any distortions in a reflection of a grid pattern indicate unevenness that I can see but can't measure. I think OSR is very much a similar situation. My 2 cents.

Bob