A friend of mine is writing a story which takes place in about 1775. At one point, one of the characters hears someone fire a shot using a Brown Bess (British military musket) from a distance of perhaps half a mile. She does not have a clear line of sight back to the shooter, who is behind her. Perhaps her vision is blocked by trees or a hill.
How loud would the shot sound to her? What would it sound like? A comparison to a modern-day noise is acceptable.