Some quantities were stored, but most was broken up and reclaimed. Meaning the cartridges were broken open to reclaim the black powder for other uses and the bullets were melted down and recast.
This was done with Williams type III cartridges even before the war ended. They were eventually found to be inferior, and were ordered to be broken up. Obviously many of the bullets would have been melted down, but they can frequently be found, whole, used as case shot in last-war cannon balls.