Note: In the video I mistakenly describe this as a two-stamp NFA gun. It is actually deactivated, and thus does not require a tax stamp. Sorry for the mistake!
The Swedish Bofors company developed their 40mm antiaircraft gun in the 1930s, and it would go on to be one of the most successful weapon designs in modern history. Used by both sides in WWII and in all theaters, improved versions of the 40mm Bofors gun continue to serve in military front lines to this very day. In the US, they comprise part of the armament on the AC-130 Spectre gunships, for example.
This particular gun is a WW2 vintage piece, made in Sweden. Most of the examples used by the United States were made under license by Chrysler, the car company. Something like 60,000 were produced during the war, mostly for naval use. These guns would be a mainstay of American vessels’ air defense against Japanese Kamikaze attacks.