This is a 10-22 receiver. By US law, this is considered a firearm. If you bring this item to a "gun-free" zone, you would be guilty of a felony. In case of Browning M1919 machine gun, the "firearm" is merely a flat rectangular sideplate with a serial number, no different from any other sheet of steel except for the serial number.
By US law, this muffler for rimfire cartridges is also considered a firearm. So bringing this tube with baffles to a school would also be a felony.
If two people own the same model muffler and accidentally swap them at the range, nominally they are both guilty of crimes for turning a restricted item over to somebody else - even though neither person gained any new capability from the act nor harmed anyone.
A friend emailed me this picture. DIAS stands for drop-in auto sear, it's a part of a trigger mechanism. Possession of this tiny piece of metal which has to be made before 1986 without registration and payment of $ 200 excise tax is a felony, same as an unregistered machine gun. And yet it's just a part so simple that putting it with bolts and fixtures on a hardware store shelf wouldn't attract any attention.
***The examples I bring up are obscure trivia, but they can and sometimes do lead to real prison terms and felony criminal records, and to lifetime loss of voting rights. Gun control treats guns as black magic fetishes. It's not clear how having a flash hider on a rifle harms the public more than having a muzzle brake, or how having a 15.9 "barrel harms people more than having a 16.1" barrel, or ... the examples are countless. The entire concept of prosecuting innocent possession instead of harmful actions is actively malicious because it ruins real lives over imaginary offenses.