Hey Pistolero, we need more information for a proper diagnosis.
Are you shooting a Colt-pattern revolver, with the wedge that attaches the barrel to the frame?
If so, that wedge must be tight. If you can pop it out with your fingers, it's far too loose. A loose wedge will send shots all over the target, in my experience.
What model and caliber?
If it's a .44 and you're only using 20 grs of FFFG black powder or equivalent, accuracy can be bad because you seat the ball so far down in the chamber that it's got quite a leap to engage the rifling.
You using black powder or a substitute?
Ball or conical? What size ball? Conical bullets have never been as accurate for me. As for balls, I use .380 inch diameter in my .36 calibers and .457 inch in my .44s.
This is contrary to many black powder books but experience has shown me that the larger balls are more accurate by virtue of having a wider bearing surface for the rifling to grip.
Do you use a felt wad, well saturated with lubricant, between the ball and powder?
How is your trigger pull? Dan Chamberlain is right. A long, hard, creepy trigger can really throw you off.
Look for nicks in the muzzle, which can greatly affect accuracy.
Also, look for smears of lead around the forcing cone, where the ball enters the barrel. This can indicate a chamber that is not well-aligned with the barrel.
There are many variables.
Give us all the details you can and we'll see what we can figure out.