a piece of window glass with a light coat of paper ink ( same as use for news paper or artist work ) you roll your bullet on the window glass and ink print the bearing surface after you can easy measure with a caliper or a rule
this method allow you to show pressure ring or uncylindrical bearing surface
another way is to built a small frame for a old ( low cost or get from junk ) slide projector and display the bullet on a white wall , scale factor is easy to get with bullet lenght ratio .
Thanks for the answers gents. I am going to check out the Davidson collars listed in Sinclairs. I was just wondering what people were using. I have been shooting really good CRO bullets but want to try a different caliber and will need to measure bullets.