So, if a mechanical measuring device is the preferred devise to use for measuring barrel wall thickness (or not), what device(s) would be the recommended model to use?

Word to the wise - Never buy your wife anything with an electric cord.

Allen, I've used The Hosford gauge and the Vertically mounted point and Dial indicator, and for ease of handling, the vertically mounted rod and indicator is easier and may be more user friendly, but the Hosford leaves no chance for erroneous readings, because the barrel can only be touching the inside contact point, and nothing else. The barrel is held on a mandrel, and the gauge rides in and out, only on the contact point. It also packs away more neatly.
I think, by now, Dave spotted the error in his design, and has corrected it.

What design? Which Dave?

Me, Improvements underway.

Dave, which design and which gauge are you improving? Inquiring minds, well, you know.

Bill, See my thread "When the cats away"in this catagory. I will be making a few improvements.