
Navy Six

Allow me to extrapolate. Or some such. Percussion guns are FICKLE. They do really odd and different stuff for no apparent reason. Sometimes there is a "fix" and sometimes not.
Uberti Open Top design guns ALL have a Barrel to Arbor fitment problem. As a retired Gunsmith, I am loath to allow that condition to continue and MUST fix it. Hellgate elects to put up with it and that's OK too (not really). However, with all that hoopla, I would suggest:
Try a Rag. Well, my recommendation is to spritz a rag with PAM (HYDROGEN PEROXIDE, DENATURED ALCOHOL AND MURPHY OIL SOAP) and between each cylinder full, wipe the face of the cylinder to remove fouling. This, bye the way, is a "good thing" (quote Martha) for ANY Cap Gun.
People are Hazardous to Yer Health > Avoid 'em