Nice shooting! A quick and dirty method of measuring group size I use is simply to measure edge-to-edge and subtract bullet diameter.
Seriously, I suggest trying some Varget or RL-15 with your 68gr bullets. You can get a bit more speed out of them for longer range shooting without accuracy suffering. Not that I am in the habit of throwing around load data, but 24.5-25.0gr of Varget is a good place to look. Also, IMR 8208 XBR has gotten some good reviews, but the one person I know who tried it said the accuracy dropped off before he hit his speed goals with 75gr bullets.
Anyway, good luck and good shooting!
