Shoot it straight up, really straight, catch it in a bucket on the way down then measure the length of the marks.
What Gene said is a bit better.;)
If you're in a hurry set your caliper to the Bore size and slip it over the ogive and make a mark. To make the mark just turn the bullet slightly in the caliper. Slip it over the base and make a mark. A PITA but will do if in a hurry or are impatient waiting the stoney point order to arrive.
I use a sinclair gizmo that looks like a hex nut. and insert the bullet both ways. Not as good, easy or as fast as the stoney point method though.