Joe;
I don't really recall now just what the "Catalog" name of the idicators you described was. In the Machine shop we referred to them as "Frog Legs". As you say they are about the best it gets for measuring chamber depth.
The cheapest you can go & get adequate reliability is a 6" flexible scale. Just hold the bbl up to put the cone in a shadow & measure to the shadow by eye. With a little practise one can quite easily read it to within the 1/64" markings of the scale.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra