I have a Pedersoli 1863 Sharps in .45 caliber. With the standard Army 500 grain bullet it will print less than 6 inches at 300 yards. They are loaded from the back side with bullet then powder. I don't use paper carts, too much trouble, just pour in loose powder. Stick on a musket cap and fire.
My rifle shoots so well that I installed a vernier tang sight and front globe.
Some tricks: I use alcohol/peroxide on a chamber brush after each shot. I use a short seating rod so the bullet is seated to the same depth each shot. Powder is poured in loose and the breach block cuts off the excess.
Bullet gets a 1/4 inch bees wax cookie followed by a milk carton wad. This reduced the powder charge a bit and the gun likes it so I do it. Don't know if it's the extra lube or the reduction in powder, but it shrank my groups.
The old Sharps is a fun gun to experiment with.
Bill