The M240B is the current medium machine gun in use with the U.S. Armed Forces. It is slowly replacing the M60 series in fixed, vehicle, and infantry roles. Under the designation MAG-58, the same weapon is in use with various countries around the world as a reliable, proven general-purpose machine gun. Given the large numbers of M240/MAG-58 weapons produced, why are only a handful (rumored to be only 12) available to civilians ("transferable")?

The answer is due to the laws regulating the importation and manufacture of fully-automatic weapons for U.S. civilians. The Gun Control Act of 1968 stopped the importation of machine guns for civilians, but a machine gun manufactured in the U.S. could be registered with the Bureau of Alcohol, Tobacco, Firearms, and Explosives (BATF), and then sold to civilians. On 19 May 1986, the manufacture of new machine guns for sale to civilians was banned, regardless of where the weapon was built.

The MAG-58 was originally developed in the 1950s by FN Herstal in Belgium. However, the MAG-58 was not adopted by the U.S. military (as the M240) until the late 1970s for vehicle use (it was not until the late 1990s that the M240B/M240G infantry variants were introduced to the U.S. miltary). Due to this 20+ year lag, no M240s (as MAG-58s) were imported to the U.S. before the 1968 import ban. FN Herstal, the designer of the MAG-58/M240, created a U.S.-based manufacturing company to produce the M240 after it's selection by the U.S. military (a stipulation of the contract award) in 1980; this company is FN Manufacturing, Inc. (FNMI). Hence, all M240s are built in the U.S., but production didn't start until 1980-81, when the FNMI plant in Columbia, S.C. was completed.

With the total ban on new civilian machine guns in 1986, there is a total of about 5 years (1980-19 May 1986) when a transferable M240 could have been built in the U.S. During this window of opportunity, only a few M240 machine guns were made available for sale to civilians; most went to military customers, and never reached the civilian market. These few transferable weapons are still available, if you can find one for sale.