indybrad:
The military NEVER released any M2 carbines to any civilians other than a few law enforcement agencies, which is how the very few that did get into civilian ownership came about.
The police agencies traded them in to law enforcement dealers for newer rifles and the dealers sold a few to qualified individuals.
The feeling of the military and the US Government is, "Once a machine gun, ALWAYS a machine gun".
For this reason ANY Carbine with an "M2" stamp on the receiver is ILLEGAL unless it's been properly registered with the BATF.
If it's not registered, it cannot be registered now, and it CANNOT be made "legal" by any means.
To be clear: If someone has a Carbine with the M2 stamp, even if it's nothing but a bare receiver with no parts, it's an illegal machine gun, and a State or Federal prosecutor will very happily put you in prison for 10 years for possession of an unregistered automatic weapon.
Today, with a lot of old vets passing on, people are opening up foot lockers and closets and finding all kinds of weapons and even explosives.
The best way to deal with an M2 Carbine is to strip all the parts off the Carbine and either cut the receiver up, or turn it in to the BATF.
You can legally use the parts to build a new Carbine with a surplus M1 Carbine receiver.
The military did convert M1 carbines to M2 full auto, then converted them back to M1's when they surplussed them.
A converted Carbine will have a M2 op rod, which has a "notch" on the Right side of the "box" that rides in the barrel grooves.
There may be an M2 Trigger guard which has a cut in the left side for the trip lever to fit in.
Most all other M2 parts were removed before being sold off.