The answer to Clif Morton's question, "Is the NRA right?" The NRA is right because by limiting magazine capacity they in a sense ban those firearms. Many firearms come standard with magazines over 10-round capacities. If that firearm is no longer made, where do you get a 10-rounder for it? AR-15s come standard with 20- and 30-round magazines. Those are not high-capacity magazines, they are standard-capacity magazines. Many pistols come standard with magazines from 13- to 19-round magazines, or even higher. Ten-rounders are not made for them.
Magazines are designed around the pistol's grip, and the capacity ends up to be whatever. Sure they could make a magazine to reduce the capacity from 19 to 10. But then the price of that magazine just triples because of the special follower and spring it would need. And if that firearm is no longer made, then what? Yep. You got it. Some bureaucrat is going to make it illegal and make you a felon. And that is exactly what is happening in New York where they went to a seven-round limit. Many rifles have eight-round inblock clips, or standard fixed 10-round magazines. Those can't be changed. Now New York want those firearms.