In 1934, the National Firearms Act was approved and passed by congress, and the expensive tax of $200 was set on any legal purchase of the certain items listed in the bill. At that time, $200 was far more expensive than any item that was purchased, making it almost impossible for a citizen with an average income to acquire.
This act of congress (which many gun enthusiasts find aggravating) restricts the following: a shotgun having a barrel of less than eighteen inches; a rifle having a barrel length less than sixteen inches; or any other weapon, other than a pistol or revolver, from which a shot is discharged by an explosive if such weapon is capable of being concealed on the person; or a machinegun. This act also restricts a muffler or silencer for any firearm, whether or not such a firearm is included in the foregoing definition. The NFA branch of the BATFE regulates the registration and restrictions of such items and classifies a silencer, suppressor, muffler, or moderator as a device that decreases the sound signature of a weapon.
In the same article, poaching was a large issue in the great depression, it and the mob issue was why silencers got on the list.
