Anyone remember that one Hamas dude who became a very good sniper using an old M1 lol.
Resistance movements still use even older rifles like the Mosin Nagant. Banning the AR-15 isn't going to accomplish anything of value.
I think a way funnier and better option would be to require marksmanship exams that you have to pass in order to have a license for rifles and shotguns. A hilariously large amount of people would fail to qualify.
And make it expensive so it immediately disuades anyone trying to get a capable firearm quickly.