I have a set of turned brass gauges I use in the shop. For portable use the best I think is an inside dial caliper like the one below. You can see exactly where the forcing cones start it also will work as a quick choke measuring tool. Its leg length is 3.25" and will measure from .375 to 1". I bought mine 20 years ago when they were cheap, Enco has them for around 80.00, you might find on on ebay for a lot less.

Jim


I learn something every day, and a lot of times it's that what I learned the day before was wrong