Certain states require that a fired cartridge case be submitted to their "ballistic fingerprint" database when a pistol is purchased in that state. Most/all manufacturers simply include a fired casing with all new pistols to avoid needing separate SKUs for those states.
If you lived in a state with one of those databases, the FFL would have taken the little envelope out of the box when you bought the gun and sent it into the state forensics lab for cataloging.
Certain states require that a fired cartridge case be submitted to their "ballistic fingerprint" database when a pistol is purchased in that state. Most/all manufacturers simply include a fired casing with all new pistols to avoid needing separate SKUs for those states.
If you lived in a state with one of those databases, the FFL would have taken the little envelope out of the box when you bought the gun and sent it into the state forensics lab for cataloging.