You have got to be kidding, a Larson or Motorola 3/4 inch MNO mount hole saw with two groves across the face are the best thing. The thing that the hole punches do not do, and for that matter, most of the hole saw's do not (with out the groves), is to provide a good ground. No ground, no work. All law's of antenna's prove this. A typical NMO mount has some feet, but they do not penetrate the under side of a vehicles roof satisfactorily to provide a good ground. The grooves clear the paint around the brass and will make your antenna work very well. 100% automatic if after you make the hole, hold on the trigger for a few more seconds. You can also use the saw to clean a badly punched hole.
Make sure to be center…
Mike