Tazman,
If the gun really hasn't been shot much, a 2" group at 100yds is probably the best you can expect. It took about 100 rounds and 2 dozen patched round balls before my gun really came into its own.
To start, it's best to stick with 1 powder type & 1 bullet type. Shoot 3 shot groups at each increment of 5gr of powder: 90gr...95gr...100gr...105gr...110gr...115gr..120gr . If none of these come close, then it's time to try the same proceedure with a different bullet, or at least one of the same type at a different weight.
If you can't get where you want to be after 2 or 3 different bullet combinations......the barrel may need a little break-in work. Spend a day shooting patched round balls (.490dia ball with a .10 or .15 thick patch) over about 80gr of powder - I would say shoot 25 to 50 of them. Don't worry too much about accuracy - maybe practice some off-hand shooting at 25yds while you're doing it.
After doing that, I'd be willing to bet that if you started the load work-up process back at the beginning, that you'll see a significant change in accuracy. I know I did in my Knight.
Also, 1 last tip when shooting for accuracy: run a spit-soaked cleaning patch down the barrel after each shot (maybe 2 patches if using Pyrodex or true Black Powder). This keeps the barrel consistant and eliminates that from the equation of figuring out where the accuracy is going.
All this sounds like kind of a pain, but when you get that 1 load that cuts holes every shot........What A Rush!! <img src=icon_smile_big.gif border=0 align=middle> <img src=icon_smile_big.gif border=0 align=middle>
"Every moving thing that liveth, I give unto you as meat" (Gen 9:3)
Trust God..........but keep your powder dry!