Police have determined the stray bullet came from a fish and game range near Lethbridge, where two men were target shooting with pistols last month.
The bullet cleared the safety berm when one of the men inadvertently fired the pistol while the barrel was pointed upwards.
Officers were called to a north-side home where the residents heard a bang, found a hole in their ceiling and a bullet on the floor.
No one was injured.
Police say the men at the range co-operated completely and the man's actions have been deemed non-criminal.