Measuring Bore Size

Question
This question has probably been answered before, but I have been unable to construct an accurate search.  I believe that I have seen a method to measure the bore size of older handguns that involves pushing a dummy wax bullet through the bore.  If this is a valid approach, how does one accomplish it?

Answer
I'm not sure if wax would be dimensionally stable enough. I can't say it IS not, just that I'm not sure.

The method I have seen involves taking a slightly oversized slug of VERY soft led and pushing it through the bore so that it is swaged thought the bore (called "slugging the bore"), then measuring it at the narrowest (from lands-to-lands marks) and the widest (groove-to-groove marks). You would want your projectiles to not be any wider than the widest point slugged.