With muzzleloaders, as well as any firearm, effective range depends on the gun as well as the shooter. I have taken several deer with my scoped TC Black Diamond and my TC Triumph at 100 yards give or take. These guns are 1-28 twist and I use 100grains of 777 and 240 grain .45 cal pistol bullets with Harvester crush rib sabots. Both are sighted in to zero at 100 yds. Usually they drop in their tracks,
With my 1-60 twist cap-lock I have hit and lost several deer trying to shoot past 50yds. I now pretty much try to get within 30 yds if i hunt with that gun. Not so much because of the gun, but because my vision is no longer suited for shooting open sights. That is,the front sight is blurry
My 1-32 twist flintlock is inherently more accurate than the cap lock. The limiting factor is me the shooter because of the vision issue.
On my bow I have a peep site called a Verifier. It has a diopter lense that clears up the image of the sight pins leaving the target blurry. I have looked for a peep site with this option for the flintlock and cap lock with no luck. If I had it I could improve shot groups increasing the effective range .
With open sights it is very difficult to get a good sight picture past 75 yds even with 20-20 vision. At that distance it becomes very difficult to pick a spot because the sight blade starts to cover the whole animal. IMO shots past 75 yds with open sights are unethical.