I have a t/c flinter made in 1977 50 cal. and it will tack drive R/B with high charges of 3F Goex 90 to 100 grains of powder.I would say the shallow lands in the t/c barrel (or I should say Douglas barrel) seem not to shoot that well with light powder charges.
I tried a few lead bullet/sabot in the flinter 325 gr. 260 gr. lead sabot bullet with 85 gr. of F goex all I can say it also tack drives these bullets into the same hole.
My flinter is set up with a rear peep sight,I use to late season hunt the PA. season but I use a 54 cal. renegade that had open sight :again built from a kit Gun back in the 70.'s
I finished last year a but together renegade 54 flinter with a 1 in 66 twist 230 gr R/B behind 95 Gr. of 3F goex and it a tack driver.