Oh, check this article out:
http://www.snipersparadise.com/tsmag/July03/july03.htm

because it has a test in it that I believe you are performing. Your just doing an experimental design, is the only difference.

and in particular this chart:
http://www.snipersparadise.com/tsmag/July03/TSD%20Wound%20Chart-MZ.xls

and if you don't have Excel, I have screen capture this from reseach I did a few years back:

http://www.the-gleasons.com/TSD%20Wound%20Chart-MZ.htm

Anyway, hope that is helpful. Chap