From Field & Stream:
This video shows what must be the worldâ€™s largest shotgun shell: the 120mm canister round designed for the cannon of an M1 Abrams tank. The 50 pound shell contains 1150 .40 caliber tungsten pellets launched at 4500 fps, with an effective range of 500 yards.
Whatâ€™s fascinating to me is that you can see clearly that the shot charge of the canister round behaves exactly like a load of shotgun pellets. As the round leaves the muzzle, the pellets at the front of the pattern encounter air resistance and begin to peel off and fall behind the main charge, opening the pattern and forming a shot string. The pellets to the rear of the shot column draft behind the leaders, retaining velocity and moving to the front. The canister flies with the pattern for quite a ways (our light plastic shotcups have petals that open open and slow the cup quickly). Eventually, though, the poor aerodymic shape of the canister causes it to slow down, and you can see the trailing pellets catching up and passing it in flight.