Shoot a group.
Find the 2 holes that are the farthest apart and measure center to center in inches.
If you shot the group at 617 yds, divide by 6.17.
That's basically your MOA spread for that group.
Shoot another group and do the same thing again to get the MOA extreme spread for that group.
Do it again several times and then average the MOA for all the groups.
You don't just average the distance for each consecutive shot fired.
If the numbers get too large, just ignore the ones you don't like and call them fliers. Or, make up an excuse about the wind or something. That's what a whole lot of people do.
If you shot a 3 shot group that was 1/2 MOA, then you shot one good group.
When you can consistently shoot 5 shot groups that average 1/2 MOA without ever having fliers, then you're developing consistency and confidence.
For the most part, you only have to please yourself. When you think you have something to prove, enter a competition.
Happy hunting!