Proposal to become law; some details I'm sure need to be ironed out, but here goes (and this is only part of what I desire in reform).
For Manufacturers:
As of June 1, 2019, whatever you are currently producing, you can continue to produce. However, any new designs/new guns in the works, all those plans must be scrapped.
You cannot enhance the weapons in production as far as performance. You can enhance safety features, however.
If you currently offer options for magazine size, the smallest one becomes the only option for purchase. (Model X can have a 9-, 15-, or 20-round mag, so 9-round stays, the rest go).
You can enhance weapons cosmetically (pearl handles, gold-plated, My Little Pony themed, etc), as long as the performance is not enhanced.
All of the above will be termed "Factory Standard." I chose a past date, so the manufacturers cannot change a bunch of stuff at the last minute to skirt the new regulations.
Now, for the gun owners/buyers:
ANY after-market modification is now illegal, cosmetic or otherwise. Whatever you bought from the manufacturer/shop/etc, that's how it's going to be, period. No exceptions (which eliminates all the what-ifs and what-abouts).
If you have a modified gun, which includes larger than Factory Standard magazines, you must revert your weapon back to Factory Standard specs.
If you cannot revert, weapon must be surrendered.***
Punishment (and I'm open for suggestions):
$1000/per weapon AND 100 hours of community service in a year's time.
$1000-$5000 AND 100 hours of community service in a year's time.
The reason for those punishments, is there's a better chance of getting the money, prisons are too crowded, so make them improve the community they live in.
***Now, about surrendering the weapon. Here's the chance for a buyback/exchange, etc. The manufacturers could score big points on this if they offer to take in the modified weapon, and replace it with the same/equivalent non-modified weapon. No one loses their guns, Factory Standard makes each model uniform in performance.
The above requires everyone to give a little, and they also get a little back. You now have limits on clip sizes, performance mods are gone, no "bigger better faster" gun will be produced (at least for the public; armed forces are obviously a different story).