Guns have three purposes: target shooting, hunting and killing people.
As a young man, my father made me hunt with a single-shot rifle, saying that a competent hunter only needs one shot. No skilled hunter needs more than five shots and the best target guns are all single shots.
So the only use of a high-capacity magazine is to kill people -- or satisfy a big ego.
When I was young, there were few semi-automatic weapons. We hunted with guns that had to be cocked or reloaded with each shot. If we had laws restricting magazines to five shots or guns that had to be cocked between shots, it would be difficult for a gunman to take down scores of people before someone tackled him.
While other new laws are necessary, this would not have any effect on law-abiding hunters and target shooters -- it only reduces military type carnage in our cities.
If you are a true sportsman, you don't need semi-automatic weapons with high-capacity clips.