Telling When Scope has Gone Bad

Aside from any obvious things, how can one tell when a scope has gone bad?

If you shoot a number of rounds without changing the adjusters or the point of aim, a bad scope will start to show two or three separate groups, sometimes in a triangular shape. Each impact point will form a group, if enough rounds are fired. But the slug impact will move from one to the other group in between shots. Shots that continually go against the wind is another good indication…