In yUK and in other international competitions we shoot percussion rifles out to ranges of 1200 yards. AND make decent scores. Take a look at long range muzzleloading rifle shooting. No optics are permitted, just elaborate tang sights. Incidentally, we shoot OPEN-sights out to 900 yards.
This is our 1200 yard range - Stickledown - at Bisley National Shooting Centre -
Just like with any rifle...
Take the time to learn the rifle and its preferred load and you will hit with it.
A quality muzzleloading rifle is capable of amazing accuracy at many different distances...far more than popular "knowledge" / wisdom , gives them credit for.
Whether or not the shooter of the same , is capable of that degree of accuracy is open to question....