The Musket was used in large formations against other massed units.
So if the original target is not hit there is a chance that the guy behind will be hit.
The Rifle on the other hand was used in small skirmish groups.
https://en.wikipedia.org/wiki/Baker_rifle
Accuracy for the Musket was good for 80yards but required volley shooting to hit the enemy.
The Rifle was good between ranges of 100-300yards. Deployed to take out opposing skirmishers before getting on with their main duty of sniping off various officers.
Using cover was a must.