What I do, which may not be 100% correct but closer than posted:
(1) A 6mm bullet does NOT make a 6mm hole in paper.
(2) Measuring to the "edge of tear" is not reliable at all. Measuring to edge of black is much better. Best is getting the device Charles mentioned.
After deciding to report accurate measurements, you shoot a single hole, measure edge of black to edge of black and subtract that from your overall edge of black to edge of black measurement for the group.
Don't particularly give a rats a$$ about this gun or this group but going back to the basics of the Internet, if you post a pic be ready to defend it.
when you come down to it, its all guess work, with the tools we have we can get a different measurement each time used, and I am familiar with the tools that Charles is talking about. its a matter of how far you want to take it. the holes will look and be completely different from point blank to 1000 yard targets. Why should he have to defend it? if you don't give a rats ass then don't post or get involved, he has nothing to prove to you or me. He is just glad to be involved and gain knowledge and skills to improve his game. Ron Tilley