There was a case where a man was accused of illegal possession of a machine gun for having an M-14 rifle that had been modified to make it into a semiautomatic rifle. The ATF agent testified that he was able to readily convert the rifle into a machine gun. Read on:
I examined (the firearm) and determined that it was originally manufactured as a machinegun by the Winchester Company in New Haven, Connecticut. (The rifle) can accept machinegun components and has machinegun components installed, but the engagement surface of the sear release has been removed, and the sear release has been welded to the selector shaft. In this condition, (the rifle) is functional as a semi-automatic firearm, but the machinegun parts have been locked in place by the welded sear release/selector shaft.The jury disagreed that replacing the entire fire control group fit the definition of "readily convertible" and found the man not guilty.The man's name was Albert K. Kwan
To determine if (the rifle) could be readily restored to shoot in an automatic manner, I used a multipurpose rotary tool with a cutting wheel to cut through the sear release. I then removed the sear release, selector shaft, and selector-shaft lock from (the rifle) and installed a sear release, selector shaft, selector spring, and selector from an M-14 machinegun.
The technician did not modify the receiver during all of reassembly, and then fired the gun to see if it would fire full auto. At that point, he wrote, "I discovered that the sear ... did not have an engagement surface for the sear release." So, he replaced the trigger group of the rifle with another trigger group which contained the sear with an engagement surface and eventually got the rifle to fire three rounds with a single press of the trigger.