Sounds similar to the .725" bore'd "Fluid Steel" double I shortened to 24" (or was it 26") and put express sights on. My best loads used round balls - best accuracy and performance running 1,500fps with .715 balls(545gr.) and .684" balls(484gr.) & specific wadding - mostly tabulated on another post-thread about loading slugs.
; Lee and Lyman both have .690" moulds and Lyman has .715"RB's.
: If your gun is over=bored, it may have .735" bores and Lyman makes a .735" round ball mould.
: Jeff Tanner in England will make any size RB mould you want for $30.00US.