+1 Earl just noticed your earlier comment.

I also suggest using Shoot-n-see targets for practice it will make the holes more obvious with a quality spotter. I was able to see orange golf tees at 500yds used to mark .223 holes for military competition with a 45x Konus spotter. I would imagine shoot-n-see targets as long as they are they good contrasting ones would offer the same as the golf tee.