An impingement sleeve and methods for designing and forming an impingement sleeve are disclosed. In one embodiment, the impingement sleeve includes a body configured to at least partially surround a transition piece of the combustor. The impingement sleeve further includes a plurality of cooling holes defined in the body, the plurality of cooling holes having a cooling hole pattern configured to provide a desired operational value for the transition piece. At least one of the plurality of cooling holes has a chamfer extending at least partially between an inlet and an outlet of the at least one of the plurality of cooling holes. At least a portion of the plurality of cooling holes are generally longitudinally asymmetric.