Re: moa question
Shooting at an angle will reduce the amount of MOA needed. I am shooting a 162 amax at 3060 fps, zeroed at 100 yds. 550 yds needs 9.0 MOA, 550 yds at 20 degrees needs 8.2 MOA. That is 0.8 MOA less or about 4 inches less drop. So without correcting for angle a shot would be 4 inches high.
If you only need 8.5 MOA for 550 yds then you would probably be a little less than 4 inches high without correcting for the angle.
In the field angles are usually less than they seem, did you actually measure the angle or did you estimate it? Under 15 degrees the difference at 550 yds would only be an inch or two.
I'd call it good shot rather than luck, but you do need to measure and correct for the angle, particularly once the range gets out there. There are some good threads on here on correcting for angle.
Hope this helps, it got a bit long winded.