Was a victim of that. Was shooting a pretty much normal for me trap round in the low 20s and felt like shooting another round. Shot a 7 with no idea why. Everything felt right. Had a friend and fellow 4-H instructor help (a knowledgeable spotter is an essential) and he couldn't spot the problem. Finally, after a couple weeks of mystery, figured out my left eye was trying to be dominant while looking at distant hills (silos actually) through the sliding glass door in early twilight. Came on just that suddenly and forcefully.
