But, ARs can be cheap or expensive. Optics, too. The grenade launcher would require a tax stamp..
How about this: Repeal all laws on "silencers."
The laws are based on a false premise (that they actually silence a firearm...thanks, Hollywood), and they just make sure that anyone who uses a firearm in self defense (and all their nearby loved ones...e.g. all the kids in the house), experience permanent hearing loss for no reason. They are still loud with a suppressor, but the hearing loss will be substantially reduced.
And, as an added bonus for Chris (who used to push for regulation on those evil fast bullets...which was a thing for the gun control lobby for a while), most people with suppressors would start buying sub-sonic rounds to further reduce the noise...no need for regulation.