Spent projectile found in Sydney yard

Police have found what they believe is a spent bullet in the yard of a house in Sydney's southwest after the occupants reported hearing what they thought was a firecracker going off.

The projectile was found at about 2pm(AEDT) on Saturday after police were called to the house in Casula.

Police have sent the projectile off for forensic analysis and say it appears to have been fired, but the house appeared to be undamaged.

A police spokeswoman told AAP the occupants said they heard what they thought was a firecracker going off the previous night.

Police are urging anyone who might have information leading to the person responsible to call Crime Stoppers on 1800 333 000.