Hi Ear, Maybe try the TC Bore Butter? So you are using "sabot" slugs? Save some money and try plain old Win, Rem or Federal slugs. I find these soft lead slugs work really well with the RCT, I just like the Winchester Super X ones better.
As to your question, If I did'nt swab the barrel the groups just were'nt as tight than the 2.0" groups @ 50yds I was getting. Maybe 3-4" at 50yds which would open up at 100yds to more than double. With iron sights I don't want to chance a 'gut' shot or worse...so with the RCT I felt more confident at 100yds if I had to...