your ignition I suspect to a bad nipple and worthless caps. Also sometimes when people swab traditional rifles, they get them too wet and end up pushing crub against the bolster area of the rifle, covering the fire snail.

Try swabbing with alcohol. LIGHTLY dampen the patch and work it in short strokes down the bore. Then a couple dry ones. If you have any doubt of the moisture, pop a cap before you load.

There were a lot of roundball rifles out there. 1-66 was a common twist for them.