Hi Ranger
1st Question: Have you tried the t/c maxi balls out of that gun? My renegade shoots 2" groups at 50yds with the Maxi balls. My renegade didn't do so well with the power belts.
2d Question: I started shooting hornady pa conicals this year due to recommendations from other hunters. hornady says they will shoot out of a slow or fast twist barrel. They shoot very accurately out of both my hawkens and rengade with 1:48" twist. I have friends that say they shoot accurately out of their 1:60" twist barrels. I would try some of these conicals before you give up on this barrel.
The renegades have 1" barrels , Thompson center and green mountain barrels have 15/16" barrels on their 50 cal. barrels, which will make a loose fit. on your renegade. Like I said maybe try some of these other conicals, you might find a winner.
Hope everything works out for you.