Admittedly I only have handguns, until they were lost when my fishing boat capsized, but when I started going to the range several years ago I'm standing perfectly still, controlled environment, lined the sight up perfectly, and at 30 yards I missed the entire target by three feet. I've since gotten better but Mrs. Burgundy is still more accurate than me.
Not surprising to me that a 20 year-old mom's basement dweller who's maybe practiced a little bit missed his target (Trump) and killed someone else. Frankly I'm surprised he winged Trump at all.
Lee Harvey Oswald was at least in the military for a while and presumably had some training.