Use scotch tape, as was said. I'm sure you know about using a stripped bolt, etc so just do that but measure the tape with a micrometer rather than guess what it is.

Yes you are right the tape is measured with a mike.
It is easier (and less messy) to stick two layers together
and measure two layers (then divide by 2). The important thing is to feel for the shoulder touching.
Good luck!

Sorry but I don't think I explained it clearly enough.

Stick pieces of tape to the back of a cartridge until a stripped bolt closes firmly, now take that stack of tape and measure the total thickness.