AS PER THE BATFE REGARDING "FLASH-BANGS"
From the November 2008 FFL Newsletter:

TRANSACTIONS IN EXPLOSIVE-TYPE DESTRUCTIVE DEVICES
ATF has been asked about the controls on firearms which also contain explosives, such as ‘flash-bang’ 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.

If you import explosive-type destructive devices, you must:

Have a Federal firearms license (FFL) as an importer of destructive devices, ammunition for destructive devices, or armor piercing ammunition (Type 11)

Pay the SOT as an importer of firearms (Class 1) Have a license as an importer of explosives unless the activity is in performance of a government contract Register under the Arms Export Control Act as an importer.

If you manufacture the explosives to be used in the manufacture of explosive-type destructive devices, you must:

Have a Federal firearms license (FFL) as a manufacturer of destructive devices, ammunition for destructive devices, or armor piercing ammunition (Type 10)

Pay the SOT as a manufacturer of firearms (Class 2)

Have a license as a manufacturer of explosives unless the activity is in performance of a government contract.

 Have a Federal firearms license (FFL) as a manufacturer of destructive devices, ammunition for destructive devices or armor piercing ammunition (Type 10)

Pay the SOT as a manufacturer of firearms (Class 2) Have a license as a dealer in explosives unless the activity is in performance of a Government contract.

If you deal in explosive-type destructive devices, you must:
Have a Federal firearms license (FFL) as a dealer or manufacturer in destructive devices (Type 09/Type 10)

Pay the SOT as a dealer or manufacturer in firearms (Class 3/Class 2)

Have a license as a dealer in explosives unless the activity is in performance of a Government contract In limited circumstances, a person could acquire explosive-type destructive devices by having a permit as a user of high explosives. The acquisition would only be for the person’s own business use or interstate transport.

AGENCIES TAKE NOTE:
On-Board Storage of "Flash-Bang" grenades by Law enforcement Agencies as indicated above, the BATFE has maintained that "Distraction Devices" / Noise-Flash Distraction Devices / Flash Bang Grenades / "Sting-Ball" Grenades, are classified "Firearms" as well as "Explosives".
Accordingly, a padlocked .30-cal ammo can does not qualify as a "Storage Magazine" with respect to federal Explosives laws.

 18 U.S.C. 842(j): STORAGE OF EXPLOSIVES 18 U.S.C. 845(a): EXCEPTIONS; RELIEF FROM DISABILITIES 27 CFR 555.22: ALTERNATE METHODS OR PROCEDURES 27 CFR 555.29: UNLAWFUL STORAGE 27 CFR 555.141: EXEMPTIONS 27 CFR 555.205: MOVEMENT OF EXPLOSIVE MATERIALS Under Title 18, United States Code (U.S.C.), Section 842(j),
all persons must store explosive materials in compliance with the regulations issued by the Attorney General.
Held further, State and local bomb technicians and explosives response teams may store explosive materials in unattended, official response vehicles parked at an outdoor location, provided the conditions set forth below are met at all times. The outdoor location may be an unsecured area accessible by civilians or unauthorized personnel.
(1) When not in use, official response vehicles must be locked at all times and have at least one additional security feature, such as a vehicle alarm, vehicle tracking device, or vehicle immobilization mechanism, or other equivalent alternative; and
(2) Official response vehicles located at an outdoor location may not store explosive materials in excess of:
      a) 10 detonators (electric, non-electric, or electronic); and
      b) 2.5 pounds Net Explosives Weight of all other explosive materials.
[Under this clause, NO MORE THAN 10 "FLASH-BANGS" MAY BE STORED ON THE TRUCK * ATF Revenue Ruling 2012-4]

Held further, all State and local law enforcement agencies intending to store explosive materials in official response vehicles, whether attended or unattended, must meet the following criteria at all times:
(1) Explosive materials must be stored in at least a Type-3 magazine; [There is NO exceptions]
(2) Magazines must be secured with one steel padlock (which need not be protected by a steel hood) having at least five tumblers and a case-hardened shackle of at least 3/8-inch diameter.    
Alternatively, the magazine may be secured by placing it inside a locked compartment within the vehicle designed to meet law enforcement construction standards for weapons storage within the vehicle;
(3) Agencies must securely bolt or otherwise affix the magazines, or the locked compartments in which the magazines are stored, to the vehicle. Nuts must be located on the inside of the magazine or compartment where they cannot be removed from the outside. The nuts must be covered with a non-sparking material, such as epoxy paint or plywood;
(4) If a magazine placed in a vehicle uses a secondary locking system containing a chain or cable and a padlock, the agency need not bolt it to the trunk or cargo area of the vehicle or lock it with one steel padlock. Rather, the agency must close and stabilize the magazine securely within the trunk or cargo area of the vehicle using the secondary lock’s chain or cable and padlock;

Officers storing explosive materials within official response vehicles must maintain an inventory storage record. The record must contain the name of the explosive material’s manufacturer, the quantity on hand, and the dates that the materials are received, removed, or used. Officers must maintain a copy of this record within the vehicle and at an off-site location, such as with the Bomb Squad Commander;

 Officers must conduct a quarterly inventory of the explosive materials on hand and compare it to the inventory storage record. Officers must note this inventory in the inventory storage record; Officers must inspect the magazine once every 7 days to determine whether there has been any attempted or unauthorized entry into the magazine, or unauthorized removal of the contents stored in the magazine