This Politico article is well worth reading in full. But there are a few things I found helpful:
Explanation of how gun features work
The newly reintroduced Assault Weapons Ban is emblematic of gun control proponents’ consistent failure to understand how gun technology and the gun market actually work in the 21st century. Gun bans that are based on outlawing certain firearm features (like the vertical foregrip or the adjustable stock) or limiting guns’ capabilities (for instance, by limiting the number of rounds of ammunition they can hold) are relics of a bygone era when you bought a gun and didn’t modify it without the help of a professional gunsmith.
For modern firearms, the “gun” from the perspective of federal law is typically an empty (and increasingly 3D-printable) metal frame or polymer shell with a serial number stamped into it, while all the rest of the parts that actually make the gun work are widely available online to anyone with a credit card.
The simplicity of the proposal - even I can understand it
A federal license for all semi-automatic firearms would rest on two simple and well-defined concepts, one technical and one legal:
1) A “semi-automatic” firearm is one that fires a single round for each pull of the trigger, automatically reloading in between each shot until the ammo is depleted.
2) “Possession” is a legal concept from the drug war that implies that a person has a contraband item “on or about one’s person,” or has “control” over the item, perhaps by having it in a motor vehicle or in a home.
Because both of these things—“possession” and “semi-automatic weapons”—are easy to define, they're easy to regulate.
Under a licensing regime that authorizes license holders for possession of semi-autos, it doesn’t matter whose semi-auto you’re holding, where you got it, how big the magazine is, or how terrifying it looks to the New York Times editorial board. It only matters that you’ve been vetted and are licensed to possess this category of weapon.
As I said, read the article in full for yourself. It specifically addresses objections that would be bought up by both the pro and anti gun sides of the debate.
Please let me know what you think? Would it work? Is it a good idea? Does it have fatal flaws?