The biggest hindrance to long range muzzies is the sighting system if you can't use a scope.
I joined RS back when I primarily hunted ML in a state that required all lead bullets, loose powder, cap ignition and open sights at the time, hence my handle.
I found peep sights to be the way. A Williams WGRS rear peep is OK, the target sights are even better. the target sight can be used to dial for distance like a scope.
The front sight needs a fine point of aim. I like the KNS crosshair sight, a Lyman globe or the Williams Western Precision globe.
After you have sights worked out. you need to find a load that is accurate. Start by weighing your charges on a good scale. I've found volume is frequently off by 10%(black powder/pyrodex)
weight and volume ARE NOT THE SAME. measure ten by volume, then weigh those and get an average to go forward.
Then find a bullet it likes that fits the regulations you have to meet.
Then shoot it and learn it's personality. How many shots can you go before cleaning the barrel etc.
My most accurate Muzzy was an Omega. w/140gr Pyrodex RS and a Hornady 225gr .452 FTX in a Black sabot, it would shoot 4" or less @ 250 yds. I never got to put it on paper beyond 250. The regulations changed and I got to hunt with the sabot combination 1 year. I killed an elk and a deer.
Then I moved to a state with no incentive to hunt with a muzzy for several years.
You could look up Gibbs rifles and paper patch bullets.
I'm about to build a Gibbs style rifle with the intent to have a primitive legal muzzy that will legitimately shoot well enough to hunt with out to 500yds.