If OSR is visible, then it is measurable. You would just need equipment with the appropriate sensitivity. I'm not an engineer, so have no idea what that equipment might be.
Whether OSR is of mechanical consequence or not, it is of consequence to the owner of the rifle, not least in terms of value. Guarantees are admirable and show the manufacturer's faith in their product, but of zero value on a non-replaceable item - new barrels on an old DR destroy the originality. That's why proof is important. Bullet makers offer no proof OSR is not possible with their bullets, just the same as owners of DRs with OSR are accused of offering no proof because they can't photograph or measure it. Doesn't mean it isn't there or that it is of no consequence though.