Anyway, I put a Nikon P3 on the Matrix 380, and I wanted to have some ranging help with the scope. After verifying where my speeds line up which is totally irrelevant or separate from this advice, here is what I did. I went out in the field by my house, and took shooting sticks, my scope, and a 3D Deer target with me. I actually drove out there, but another moot point.
I set my 3D Deer at 20, 30, and 40 yards and using the sticks for balance recorded where the back of the deer was, and the chest, or lower belly lined up on my scope lines. I did this 3 times at these ranges to check it out for repeatability. We have all had deer just appear out of nowhere while hunting, and have zero chance of ranging them without getting busted. This is what motivated me to do this. I can now asses within a few yards how far the deer is using this technique. Using the cross hairs for 20 yards on the back of the deer, and the belly at 20 yards they will intersect the 20 yard cross hair, and the mid point between between the 60 yard circle, and the thick vertical center line. At 30 yards that lines up with the 20 yard cross hair, and the center of the 50 yard circle, and at 40 yards the 20 cross hair, and middle of 40 yard & 50 yard circles. It take practice, and I encourage you to use whatever scope you have to make a little sketch, and study it! This will help you make a good guess on distance in a pinch, and hopefully put that deer in the back of your truck. If you do not have a 3D deer to use you can use something 16" tall to do this, that is close enough!
Hope this makes sense, and helps someone else!
I never tried that! 
