I get questions frequently about various shells for sale and if the are legal. There are lots of shells which are illegal in the USA which end up in collector hands. The most common are explosive and incendiary rounds. Any caliber projectile which contains OVER 1/4oz. (AV.) of explosive or incendiary substance is considered a destructive device and requires a license to own. 1/4oz.(AV) is 109.38 grains or 7.08 grams. Many projectiles of 15mm or larger which are EXPLOSIVE or INCENDIARY are destructive devices under this law. This depends upon the thickness of the projectile body and this information is hard to find for most folks. In addition most who encounter such ammunition are not familar with color codes and often the color codes are missing.
This law only applies to the projectile. A live 120mm APT COMPLETE is legal to own but most 20mm LIVE explosive PROJECTILES are not, Under FEDERAL law. Laws from state to state vary.
20mms which are APHE or API usually do not fall under this law because the AP core takes up a large part of the projectile cavity.
Many artillery and bomb fuzes contain more than 1/4oz(AV.) of explosives
the government has yet to decide if the fuze is a projectile under the law.
Colorfull large caliber ammo is tempting to own but can be a major problem.
Education is the best defense.