As I said, the Stan Baker set I used performed flawlessly and accurately (double checked against a second bore gauge) on every barrel and subgauge tube I and my friend ever used them on, including multiple sets of Kolar 28ga tubes.
Mitutoyo 209-111. Will do EVERY shotgun gauge, including 410.
They are very high end, and quite expensive when new (over $300), but can usually be picked up on ebay for 60 to 80 bucks (I think I bought mine for $40 or $50 five or so years ago). Looks like there are only 2 on there now, and they are both over 100 bucks, but keep an eye on there and you should be able to get one cheaper, one sold for $60 and one for $90 back in November, guess the price/value has gone up a little bit.
Barring that, Enco has a Chinese clone of the 209-111 here: http://www.use-enco.com/CGI/INSRIT?PMAKA=612-5810&PMPXNO=951680&PARTPG=INLMK3 and its on sale for $60 currently. Personally I'd hold out for a used Mitutoyo over a new chinese one.
I set the dial on mine using the inside faces of a pair of dial calipers. It has proved to be very accurate, at least as acccurate as the Stan Baker set my friend had (I used mine normally, then borrowed my friends, and it exactly matched the measurement I came up with).
The reach is kind of short, 3.25", but unless you need to reach further into the bore than that (which you probably won't for choke measurements) you'll be fine.
Gene, I don't think 3.25 inches is enough. I'd rather have one that will reach 10-14 inches. I've used the Stan Baker type to check 12, 20, 28, and 410. The sub-gauge tubes that are hard to check are the Ultimate Ultralites with the rifling by Briley.
Gene- The only barrel that it hasn't worked in so far for me is a 11-87 trap barrel that has a pre-choke built into the bore of the barrel.
It has worked for literally every other barrel, subgauge tube, and choke I've ever needed it to, and was proven to be at least as accurate as a Stan Baker set I checked it against.
Other than that, not many chokes that are longer than 3.25" that it'd be a problem for. Even the Optimas, which are the longest production chokes I can think off of the top of my head are only 2 3/4". Yes, if you have an extended choke, you may need to screw it out and measure the choke and bore separately, but that takes all of about 15 seconds.
Obviously if you have some sort of weird taper bore, or a custom made super long choke tube, it wouldn't work, but I think it would be sufficient for 99% of applications.
Obviously a Stan Baker (no longer obtainable) or CSP 4 gauge set would be ideal, but they are also 6x-8x the price too.