Can I accurately determine the chamber diameters of a O/U with a good set of dial calipers?

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Probably, if your caliper can get a proper access to the chamber.

E-Z-Peazy on a repeater with a removeable barrel & break-open guns; not so easy on some other designs.

No, not as compared to slugging the chambers, then using GO / NO-GO gauges to check headspace. It isn't clear, at least to me, what you are trying to accomplish.

I want to hone the chambers of an O/U with a Flex-Hone and don’t want to overdo it.

As the Flex-Hone is more of a final polish than removing metal, measuring would not be necessary. Checking with Art's wouldn't be a bad idea. https://artsgunshop.com/

10-4. Thanks, guys.

I would use a telescoping bore gauge and a micrometer if I wanted to measure a chamber diameter. I do not think calipers will be very good and they will not reach very far into the chamber.

Thanks, Bill. I don't have access to those tools and would have to find a gunsmith in this area with them, no easy task these days.

$50 or $75 one Ebay would probably fix you up.

You could probably use a inexpensive snap gauge along with a mic to measure the chamber.p accurately.

That sounds like a good idea, Bama. I may do so. Thanks.

lossking: I have used a Flex-Hone for barrel and chambers on too many barrels to count. I even wore out a chamber one for 12 gauge that I had to replace. The beauty of the Flex Hone system is that you cannot over do it, and the results are always IMO uniformly excellent.

The Flex Hone removes metal via the slurry that develops. The hone is kept moving and you can after some experience feel the difference as the barrel reaches its final polish stage. It gets markedly easier to move the hone in the barrel. The little "stems" that hold the polishing grit balls do not exert much pressure.

Use it as recommended, and you can not damage anything. I personally don't see how it could remove too much metal as it only takes off the "tops" of the ridges that are formed by a reamer and stops having any effect at that point.

BTW, I have found the chamber Flex Hone to be very useful to polish the inside of my PW reloading dies. It makes their use much smoother with less effort. Yes, I am a big proponent of the Flex Hone system for final polish and only wish they were less pricey.

I've used a bore brush with 00 or 000 steel wool wrapped around the brush (and plenty of oil) chucked in an electric drill on many shotgun chambers. Works for me and seems like it should work just as well as the method shown in Randy's video.