Spotting scopes are commonly used to score targets at varying distances, but many shooters aren't sure of what is required in terms of magnification, objective size and, especially, optical quality when shooting at a given distance. How good a spotting scope is needed for 100 yard scoring as opposed to 400 yard scoring?
Before getting down to cases, there is the matter of observing conditions to consider. Air turbulence, heat mirage, dust, humidity, haze and other atmospheric conditions all affect image quality when using a shooting spotting scope and these conditions can change by the hour. There is no escape from this. Even a premium grade spotting scope for targeting shooting can be rendered useless under severe conditions of heat waves and mirage and adding more magnification or distance to the target just makes the problem worse. Before passing judgment on any spotting scope, then, it is important to make test under a variety of conditions. A lot of scopes get blamed for poor performance when, in fact, the atmosphere is the culprit.
Assuming favorable conditions, though, we can move into features and quality issues.
As for features, most shooters want an eyepiece with plenty of eye relief, because they are typically not in a position to get their eye close to the eyepiece when shooting. 15mm is a minimum, here and most shooters are happy with a bit more. For the same reason, many shooters like angled bodied spotting scopes and rotating tripod collars, which allow the scope body and hence, the eyepiece, to be rotated to various positions.