Except it isn't their property. They have a contract to operate Lake City, which is a government-owned facility. Government buys the materials and pays the contractor to produce the ammo. The contract allows for surplus ammo to be sold on the civilian market. The only way to tell the government "no" is to not re-up the contract and walk away. But then you lose 100% of the production, not just the amount sold to civilians.
I mean, in theory, it's ours... we pay the taxes for it... but in practicality, it's theirs.