Fine idea moving forward, but you have to realize there are literally hundreds of millions of 30 round mags out there already. It would not surprise me to find there are more than a billion in the US alone. Most any AR owner will have a bunch of them as they're cheap and make range time more efficient.I'm sure this has been discussed debated etc. But is it possible to limit the capacity of the magazine sold with a gun over the counter? Say like an AR-15 can be sold legally with 6 cartridge magazine. Want a larger magazine you pay a premium, go through a background search, be entered into a database and pay a tax based on the capacity of the magazine. You already have to do similar if you want to buy a silencer.
Many of these solutions would likely pay dividends many years down the road, but I suspect most folks proposing these changes aren't firearms enthusiasts who realize the mammoth numbers of these items already in circulation.