The secret to measuring chamber depth with a 6" machinist's scale is to use sight, not feel. Point the bbl toward a light sourse, as a window not real bright, with your eye behind it till you see the cone as a shadow. slide the scale in while still watching & watch for the end to just touch the shadow line, mark the end of breech wuth your thumb, pull it out & read. Take several readings to insure you are being consistent. Very quickly you will be able to acheive a measurenment with in 1/32 inch, less with more practise, amply close for determining nominal chamber length. Measurement is taken "To" the cone, not including it.
