Producing your own semiautomatic weapons isn't difficult. The Browning patents were in the public domain long before the model 1911 Browning pistol was accepted into service by the US military. For that matter, anyone with a MotoDremel tool can finish an 80% receiver.

The fact is the ship has long since sailed on gun control in the US. The FBI estimates - and they can only estimate, because no one really knows - that there are 350 million firearms in public hands in the US. Getting any meaningful percentage of those out of public hands simply isn't going to happen.