If this is a percussion gun, it will shoot 3Fg Goex better than 2Fg powder. Hold the barrel vertical so that the bore becomes a " Drop Tube", allowing the 3Fg powder to compact in the back( or bottom) of the barrel. A percussion cap injects fire into the compacted powder, and tests have shown that compacting the powder charge, using 3Fg, gives the lowest Standard Deviation of Velocity. 2Fg powder, having larger granules, does not compact as well, and therefore does not perform as well as using 3Fg. For ultimate accuracy, both granular sizes should be run through a screen to remove fines, and clinkers.
Always seat your PRB to a MARK on your Ramrod. Inconsistent seating depth can cause opened groups.
That means some cleaning needs to be done between shots, so that crud does not build up and make the chamber shorter, moving the PRB forward in the barrel. I wipe a cleaning patch on my tongue, not to get it sloppy with spit, but just to dampen it. Fold it over between your thumb and forefinger, and rub the two sides together to push the spittle into the fabric. Now open the cleaning patch, and put the wet side Down on the muzzle, centered, and run it all the way down the barrel, stopping short of the powder chamber. PUll it back out. Don't pump it.
The Second damp patch- sometimes I can simply flip over the dirty patch and use the other side, goes all the way to the powder chamber, and removes more crud. Then a drying cleaning patch goes down, sits for a couple of seconds, and is pulled back out. That will absorb any extra moisture that remained in the barrel. Now the barrel is read for the next powder charge.
I don't know how well you shoot open sights. If you have not shot open sights a lot, have another shooter, who does seem to shoot open sights well, shoot a couple of rounds off the rest with your gun. That will tell you if YOU are the problem, and not the load components.
If this gun has only fired 20 shots during its entire working life, it may need a few more shots fired through it before it settle in and begins shooting tighter groups. Try putting a business card under the barrel in the barrel mortise, and see if you can easily put the key through the barrel hanger. IF not, take the card out, and the barrel/stock fit is fine. If you can still put the key into the hanger easily, there is up and down play in the barrel/stock mortise, and you should consider bedding at least the tang and back portion of the barrel up to the first keyway. That will stabilize the barrel for better accuracy.
Finally, I am near sighted, and it only gets worse with age. I found that whether shooting open sights on my MLers, or using a peep or scope sight on modern rifles, I eliminate my own aiming errors better if I use a " Sighter" on the target.
A Sighter is a piece of paper, or a business card, stapled, or taped to the target at an angle so that one corner points to the center of my aiming point( bullseye, or 6'oclock hold). It does not matter if the sighter is mounted so that it rises up from under the bullseye, or comes down from above it. At 50 yds, where I do most of my load development, and sighting in, a business card is large enough to be easily seen against a black bullseye. At 100 yds, I take a piece of white typing paper and fold it from one corner to the opposite corner, forming a triangle. I staple that large triangle so that the point is under my bullseye. That allows me to put my front sight post against a very visible "sighter", and slowly raise the front sight up until the top of the triangle is located. Then I squeeze off the shot. Using a sighter has cut my group sizes to 1/3 of what they were with out the sighter.
Putting any black post front sight against a black bullseye is always difficult, if not impossible without stringing your shots. Pistol shooters long ago learned to hold the top of their front sights 1 inch BELOW the bottom of the bullseye, so that they could clearly see the bottom edge of the bullseye, and also see the top edge of their front sight.
The same approach can be used shooting open sights on any rifle or smoothbore. Just adjust your zero to compensate for aiming lower on the target. With an adjustable rear sight, the adjustment is done by raising the rear sight. With fixed rear sights, the adjustment is done by filing down the front sight a bit more.
Good luck. Don't give up, yet. Do actually measure the bore of that barrel, and always measure the Washed fabric for compressed thickness, using a caliper, or micrometer. You want a patch to be about 1/5 times the Depth of a groove in the barrel. Some of the T/C barrels came with deep grooves, and slow twist rifling. Others have a faster rate of twist, and more shallow rifling. You can get a RB to shoot accurately out of any ROT, and any depth of rifling, if you put together the right powder charge, and patch and lube. BUT, YOU HAVE TO KNOW what it is you have, and that always means ignoring what the factory writes on the barrel, and measuring it yourself.
Good luck. Let us know what improvements you achieve, and more details on the gun. :thumbsup:
