Reminds me of a trade gun trail I shot with a smooth bore flintlock(no rear sight) when I was buckskinnin....The last target on the trail was a vertical drinking straw at about 25yds, me and another shooter were tied and it was a hot day, our barrels were hot and mirage was very prevelent. Looking over my barrel that straw looked like a pretzel except for the very tip top, so I lined up on that well above my point of aim and took the shot, made the point that he didn't! :-D I'm not aware of any tricks other than that, ya can't hit what ya can't see.