Apparently 4 oz. is the limit. Under that = legal!
From the November 2008 ATF FFL Newsletter:
ATF has been asked about the controls on firearms which also contain explosives, such as ‘flashbang’ grenades. Firearms of this type are subject to the Gun Control Act (GCA)(Title 18, U.S.C., Chapter 44), the National Firearms Act (NFA)(Title 26, U.S.C., Chapter 53), and the Federal Explosives laws (Title 18, U.S.C., Chapter 40). Provisions of the Arms Export Control Act may also apply.In both the GCA and the NFA, a firearm is defined to include a destructive device. A destructive device is further defined (in part) as:
(a) any explosive, incendiary, or poison gas (1) bomb, (2) grenade, (3) rocket having a propellant charge of more than 4 ounces, (4) missile having an explosive or incendiary charge of more than one-quarter ounce, (5) mine, or (6) similar device;
Accordingly, this type of destructive device is not only a firearm but is also an explosive subject to all explosives regulatory provisions including specific storage, distance, licensing, and other requirements.
While there is a general exemption under the Federal explosives laws for work performed under Government contract, if you are in the business of importing, manufacturing, or dealing in explosive-type destructive devices, you will need the appropriate firearms and explosives licenses or permit and special (occupational) tax (SOT) under the NFA. If your activity is being conducted under a United States Government contract, you may apply for an exemption from the SOT
Looking at the list of items for sale and the video in the discussion —
sure looks to me like these were aerial flashbangs. Police would have fired those.
But I’m no expert.
Your link though does prove that ANTIFA could easily acquire police style munitions.
The flashbang caught in the video looks to be the large size used by police.