Blow-back

A typical example of a semi-automatic handgun that uses the blow-back principle.

I am pondering what might happen if the Federal Government decided to confiscate all semi-automatic firearms.

For one thing, the only part of the firearm that is registered is the "receiver".  Legally, the receiver is the gun.

The receiver is the part circled in red.  All of the other pieces are anonymous.  This firearm is a Hi-Point Carbine

Unless something pretty extraordinary happens, the only thing a gun owner would have to do would be turn in the receiver.  He can keep the barrel, magazines, trigger group, springs and so on.  The receiver is the part that joins them all into a functioning gun.

The evil semi-automatic pistol

Gun Control fanatics fixate on two "most evil" guns.  Those are the ill-defined "assault rifle" and the semi-automatic pistol.

Many of the semi-automatic pistols are a simple "blow back" design.  That is where the forces generated by firing the gun are reacted by "mass".  This is a very simple design.  It is the equivalent of diving off of a boat that is anchored in deep water.  The mass of the boat is enough larger that it acts, for all practical purposes as if it were solid.  Anybody with a 10th grade physics education can do the math. 

A Sten gun.  It is not pretty but it works.

Simple translates to inexpensive.  During World War II the British were stamping out "Sten" guns for about $5 a copy, approximately $70 in 2015 dollars.  It was a fully functional, 9mm machine pistol.

This "XXX-strut" costs $1.60 a foot.  It comes with holes already cut into it for triggers, magazines, etc and you can see the guide rails already preformed on the bottom of this section.  What to outlaw this stuff?  You better be ready to strip it out of every industrial building in America.  It is everywhere.  Just look up into the steel work the next time you are shopping in a Big-Box store.

The fact that the forces are reacted by mass means that the forces do not travel through the receiver and thence to the bolt.  That means the receiver is not highly stressed and non-premium materials can be used.

Attempting to confiscate all of the semi-automatic weapons in America would be an exercise in futility. Anybody with a hacksaw, a file and a catalog of coil springs can make their own.