The traditional way to do this is with a chamber gauge which is slug of steel, brass or whatever machined to the correct measurements for the muzzle end of the chamber and marked off at the appropriate distances along its length. Given the correct measurement for the gauge of gun that you want to measure, any half competent engineer with a lathe could knock you out one in about 10 minuted.
Alternatively, you can buy one from Brownells for a few $'s.
Only flaw in this simple scheme is if your chamber is over- or under size in diameter in which case you will get a false reading of depth. For example, I was measuring a gun that had had the chambers dropped yesterday and although with bore gauge I could see it had 2 3/4" chambers, the chamber gauge gave me less than 2 1/2"!
