Depends on what you mean by "accurate".
The British military used a 2' x 6' white plank as a target for their riflemen out to 300 yards in 1804. A hit anywhere on that board was considered good, for they were trying to down men, not game or to hit a bullseye.
If you want to hit a 6" target at 50 yards..., that's something else indeed.
It's basically a tight patch, usually of pillow ticking, and a decent charge. Weigh the ball you're using, then match that weight in lead #8 shot. Now adjust your powder measure to throw that amount of lead shot, and it will be set to also throw the right amount of 2Fg powder. (FYI-You can use the same setting for powder and lead shot if you want to go for squirrels or rabbits.)
Next, check the touch-hole. If the powder in the pan naturally covers the touch-hole when you prime the pan, the touch hole is too low. The touch hole should be just above the powder when a level measure of powder is in the pan. The flash from the pan is supposed to blow into the hole, not follow the powder down the hole. It may seem fast, but it does make a huge difference. If it is too low, get a gunsmith to correct it.
Then test fire for accuracy, and check the patches. If they are burned through, then the ball and patch combo isn't tight enough. If the patches are blown then gas will unevenly escape around the ball as it exits the muzzle, and will deflect the ball off target.
Good luck!
LD