I shoot my .58 flintlock with 2 felt wads.
The rifle stopped shooting well; round ball (.010 patch finger started, GM barrel).
Tried three patch thicknesses (.010, .015, .020, and 2x.010) and all were equally bad.
Fired all thicknesses with a felt wad, slightly improved.
Moved back to .010 patch but with 2 felt wads and it turned out 2" groups at 100yds.
Go figure.

Cheers and good shooting.
Tom